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<p>包含最重要概念、功能、方法等的 <a href="https://dart.dev/">Dart</a> 备忘单。初学者的完整快速参考</p>
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</svg></div><div class="menu-modal"><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#入门">入门</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#安装-dart">安装 Dart</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#windows">Windows</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#linux">Linux</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#mac">Mac</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#hellodart">hello.dart</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#windows-1">Windows</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#变量">变量</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#数据类型">数据类型</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#注释">注释</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#字符串插值">字符串插值</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" 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aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#三元操作符嵌套使用">三元操作符嵌套使用</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#控制流循环">控制流：循环</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#while-循环">while 循环</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#do-while-循环">do-while 循环</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#for-循环">for 循环</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#collections">Collections</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#lists">Lists</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#maps">Maps</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#sets">Sets</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#函数">函数</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#函数示例">函数示例</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#箭头函数-">箭头函数 (=>)</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#anonymous-lambda-functions">Anonymous (lambda) functions</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#扩展函数-extension">扩展函数 (Extension)</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#运算符重载-extension">运算符重载 (Extension)</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#类和对象">类和对象</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#类-class">类 Class</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#对象-object">对象 Object</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#构造函数">构造函数</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#抽象类">抽象类</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#getters-setters">Getters Setters</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#隐式接口">隐式接口</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#一个基本的界面">一个基本的界面</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#扩展类">扩展类</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#枚举">枚举</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#定义枚举">定义枚举</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#枚举示例">枚举示例</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#mixin">Mixin</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#定义mixin">定义Mixin</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#异常">异常</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#throw">Throw</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#catch">Catch</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#finally">Finally</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#futures">Futures</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#async-await">Async Await</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#各种各样的">各种各样的</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#null-和-null-感知">Null 和 Null 感知</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#三元运算符">三元运算符</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#条件属性访问">条件属性访问</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#扩展运算符-">扩展运算符 (...)</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#enum">enum</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#级联符号-">级联符号 (..)</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#延迟初始化">延迟初始化</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#另见">另见</a></div></div><div class="h1wrap-body"><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="入门"><a aria-hidden="true" tabindex="-1" href="#入门"><span class="icon icon-link"></span></a>入门</h2><div class="wrap-body">
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</div></div><div class="h2wrap-body"><div class="wrap h3body-exist row-span-2"><div class="wrap-header h3wrap"><h3 id="安装-dart"><a aria-hidden="true" tabindex="-1" href="#安装-dart"><span class="icon icon-link"></span></a>安装 Dart</h3><div class="wrap-body">
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<!--rehype:wrap-class=row-span-2-->
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<blockquote>
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<p>完整教程请参阅 Dart 中文社区 <a href="https://dart.cn/get-dart/">https://dart.cn/get-dart/</a></p>
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</blockquote>
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<h4 id="windows"><a aria-hidden="true" tabindex="-1" href="#windows"><span class="icon icon-link"></span></a>Windows</h4>
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<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line">C:<span class="token punctuation">\</span><span class="token operator">></span> choco <span class="token function">install</span> dart-sdk <span class="token comment"># Windows</span>
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</span></code></pre>
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<h4 id="linux"><a aria-hidden="true" tabindex="-1" href="#linux"><span class="icon icon-link"></span></a>Linux</h4>
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<p>执行以下一次性设置</p>
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<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line">$ <span class="token function">sudo</span> <span class="token function">apt-get</span> update
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</span><span class="code-line">$ <span class="token function">sudo</span> <span class="token function">apt-get</span> <span class="token function">install</span> apt-transport-https
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</span><span class="code-line">$ <span class="token function">wget</span> -qO- https://dl-ssl.google.com/linux/linux_signing_key.pub <span class="token operator">|</span> <span class="token function">sudo</span> gpg <span class="token parameter variable">--dearmor</span> <span class="token parameter variable">-o</span> /usr/share/keyrings/dart.gpg
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</span><span class="code-line">$ <span class="token builtin class-name">echo</span> <span class="token string">'deb [signed-by=/usr/share/keyrings/dart.gpg arch=amd64] https://storage.googleapis.com/download.dartlang.org/linux/debian stable main'</span> <span class="token operator">|</span> <span class="token function">sudo</span> <span class="token function">tee</span> /etc/apt/sources.list.d/dart_stable.list
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</span></code></pre>
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<p>安装 Dart SDK</p>
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<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line">$ <span class="token function">sudo</span> <span class="token function">apt-get</span> update
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</span><span class="code-line">$ <span class="token function">sudo</span> <span class="token function">apt-get</span> <span class="token function">install</span> dart
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</span></code></pre>
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<h4 id="mac"><a aria-hidden="true" tabindex="-1" href="#mac"><span class="icon icon-link"></span></a>Mac</h4>
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<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line">$ brew tap dart-lang/dart
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</span><span class="code-line">$ brew <span class="token function">install</span> dart
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</span></code></pre>
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</div></div></div><div class="wrap h3body-exist"><div class="wrap-header h3wrap"><h3 id="hellodart"><a aria-hidden="true" tabindex="-1" href="#hellodart"><span class="icon icon-link"></span></a>hello.dart</h3><div class="wrap-body">
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<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 应用执行开始的顶级函数</span>
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</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Hello World!"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印到控制台</span>
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</span><span class="code-line"><span class="token punctuation">}</span>
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</span></code></pre>
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<p>每个应用程序都有一个 <code>main()</code> 函数</p>
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<h4 id="windows-1"><a aria-hidden="true" tabindex="-1" href="#windows-1"><span class="icon icon-link"></span></a>Windows</h4>
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<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line">$ dart compile exe hellow.dart
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</span><span class="code-line">$ <span class="token function">time</span> ./hello.exe
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</span><span class="code-line">Hello World<span class="token operator">!</span>
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</span></code></pre>
|
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</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="变量"><a aria-hidden="true" tabindex="-1" href="#变量"><span class="icon icon-link"></span></a>变量</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line">int x <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span> <span class="token comment">// 显式键入</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> p <span class="token operator">=</span> <span class="token number">5</span><span class="token punctuation">;</span> <span class="token comment">// 类型推断 - 具有类型推断的通用var</span>
|
||
</span><span class="code-line"><span class="token keyword">dynamic</span> z <span class="token operator">=</span> <span class="token number">8</span><span class="token punctuation">;</span> <span class="token comment">// 变量可以采用任何类型</span>
|
||
</span><span class="code-line">z <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"cool"</span></span><span class="token punctuation">;</span> <span class="token comment">// cool</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token comment">// 如果您从不打算更改变量，请使用 final 或 const</span>
|
||
</span><span class="code-line"><span class="token comment">// 像这样的东西：</span>
|
||
</span><span class="code-line"><span class="token keyword">final</span> email <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"temid@gmail.com"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 与 var 相同，但不能重新分配</span>
|
||
</span><span class="code-line"><span class="token keyword">final</span> <span class="token class-name">String</span> email <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"temid@gmail.com"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 你不能改变价值</span>
|
||
</span><span class="code-line"><span class="token keyword">const</span> qty <span class="token operator">=</span> <span class="token number">5</span><span class="token punctuation">;</span> <span class="token comment">// 编译时常数</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist row-span-2"><div class="wrap-header h3wrap"><h3 id="数据类型"><a aria-hidden="true" tabindex="-1" href="#数据类型"><span class="icon icon-link"></span></a>数据类型</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 整数，范围 -2^63 到 2^63 - 1</span>
|
||
</span><span class="code-line">int age <span class="token operator">=</span> <span class="token number">20</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 浮点数字</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line">double height <span class="token operator">=</span> <span class="token number">1.85</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 您还可以将变量声明为 num</span>
|
||
</span><span class="code-line"><span class="token comment">// x 可以同时具有 int 和 double 值</span>
|
||
</span><span class="code-line">num x <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">x <span class="token operator">+=</span> <span class="token number">2.5</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 3.5</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token class-name">String</span> name <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"Nicola"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">bool isFavourite <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">bool isLoaded <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="注释"><a aria-hidden="true" tabindex="-1" href="#注释"><span class="icon icon-link"></span></a>注释</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 这是一条正常的单行注释</span>
|
||
</span><span class="code-line"><span class="token comment">/// 这是一个文档注释，用于文档库，</span>
|
||
</span><span class="code-line"><span class="token comment">/// 类及其成员。 IDE 和 dartdoc 等工具</span>
|
||
</span><span class="code-line"><span class="token comment">/// doc 特别注释。</span>
|
||
</span><span class="code-line"><span class="token comment">/* 也支持此类注释 */</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="字符串插值"><a aria-hidden="true" tabindex="-1" href="#字符串插值"><span class="icon icon-link"></span></a>字符串插值</h3><div class="wrap-body">
|
||
<pre class="wrap-text "><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 可以对字符串类型使用单引号或双引号</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> firstName <span class="token operator">=</span> <span class="token string-literal"><span class="token string">'Nicola'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> lastName <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"Tesla"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 可以用 $ 将变量嵌入到字符串中</span>
|
||
</span><span class="code-line"><span class="token class-name">String</span> fullName <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"</span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">firstName</span></span><span class="token string"> </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">lastName</span></span><span class="token string">"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 与 + 连接</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> name <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"Albert "</span></span> <span class="token operator">+</span> <span class="token string-literal"><span class="token string">"Einstein"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token class-name">String</span> upperCase <span class="token operator">=</span> <span class="token string-literal"><span class="token string">'</span><span class="token interpolation"><span class="token punctuation">${</span><span class="token expression">firstName<span class="token punctuation">.</span><span class="token function">toUpperCase</span><span class="token punctuation">(</span><span class="token punctuation">)</span></span><span class="token punctuation">}</span></span><span class="token string">'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span>upperCase<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: NICOLA</span>
|
||
</span></code></pre>
|
||
<!--rehype:className=wrap-text -->
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="导入-imports"><a aria-hidden="true" tabindex="-1" href="#导入-imports"><span class="icon icon-link"></span></a>导入 Imports</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 导入核心库</span>
|
||
</span><span class="code-line"><span class="token keyword">import</span> <span class="token string-literal"><span class="token string">'dart:math'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 从外部包导入库</span>
|
||
</span><span class="code-line"><span class="token keyword">import</span> <span class="token string-literal"><span class="token string">'package:test/test.dart'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 导入文件</span>
|
||
</span><span class="code-line"><span class="token keyword">import</span> <span class="token string-literal"><span class="token string">'path/to/my_other_file.dart'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 指定前缀</span>
|
||
</span><span class="code-line"><span class="token keyword">import</span> <span class="token string-literal"><span class="token string">'package:lib/lib.dart'</span></span> <span class="token operator">as</span> lib<span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token class-name"><span class="token namespace">lib<span class="token punctuation">.</span></span>Element</span> element <span class="token operator">=</span> <span class="token class-name"><span class="token namespace">lib<span class="token punctuation">.</span></span>Element</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 仅导入 foo</span>
|
||
</span><span class="code-line"><span class="token keyword">import</span> <span class="token string-literal"><span class="token string">'package:lib1/lib1.dart'</span></span> <span class="token keyword">show</span> foo<span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 不导入 foo</span>
|
||
</span><span class="code-line"><span class="token keyword">import</span> <span class="token string-literal"><span class="token string">'package:lib2/lib2.dart'</span></span> <span class="token keyword">hide</span> foo<span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 延迟导入，仅在需要时导入</span>
|
||
</span><span class="code-line"><span class="token keyword">import</span> <span class="token string-literal"><span class="token string">'package:greetings/hello.dart'</span></span> <span class="token keyword">deferred</span> <span class="token operator">as</span> hello<span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="操作符"><a aria-hidden="true" tabindex="-1" href="#操作符"><span class="icon icon-link"></span></a>操作符</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist row-span-2"><div class="wrap-header h3wrap"><h3 id="算术运算符"><a aria-hidden="true" tabindex="-1" href="#算术运算符"><span class="icon icon-link"></span></a>算术运算符</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">2</span> <span class="token operator">+</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 5</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">2</span> <span class="token operator">-</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: -1</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">2</span> <span class="token operator">*</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 6</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">5</span> <span class="token operator">/</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 2.5 - 结果是 double</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">5</span> <span class="token operator">~/</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 2 - 结果是n int</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">5</span> <span class="token operator">%</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 1 - 余</span>
|
||
</span><span class="code-line">int a <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">,</span> b<span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
<hr>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 增</span>
|
||
</span><span class="code-line">b <span class="token operator">=</span> <span class="token operator">++</span>a<span class="token punctuation">;</span> <span class="token comment">// 前增量 - 在 b 获得其值之前增加 a</span>
|
||
</span><span class="code-line">b <span class="token operator">=</span> a<span class="token operator">++</span><span class="token punctuation">;</span> <span class="token comment">// 后增量 - 在 b 获得它的值之后增加 a</span>
|
||
</span><span class="code-line"><span class="token comment">// 递</span>
|
||
</span><span class="code-line">b <span class="token operator">=</span> <span class="token operator">--</span>a<span class="token punctuation">;</span> <span class="token comment">// 前减量 - 在 b 获得它的值之前减少 a</span>
|
||
</span><span class="code-line">b <span class="token operator">=</span> a<span class="token operator">--</span><span class="token punctuation">;</span> <span class="token comment">// 后减量 - 在 b 获得它的值之后递减 a</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="逻辑运算符"><a aria-hidden="true" tabindex="-1" href="#逻辑运算符"><span class="icon icon-link"></span></a>逻辑运算符</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// !expr 反转表达式（将 false 更改为 true，反之亦然）</span>
|
||
</span><span class="code-line"><span class="token comment">// || 逻辑或</span>
|
||
</span><span class="code-line"><span class="token comment">// && 逻辑与</span>
|
||
</span><span class="code-line">bool isOutOfStock <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">int quantity <span class="token operator">=</span> <span class="token number">3</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>isOutOfStock <span class="token operator">&&</span> <span class="token punctuation">(</span>quantity <span class="token operator">==</span> <span class="token number">2</span> <span class="token operator">||</span> quantity <span class="token operator">==</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// ...Order the product...</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="等式和关系运算符"><a aria-hidden="true" tabindex="-1" href="#等式和关系运算符"><span class="icon icon-link"></span></a>等式和关系运算符</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">2</span> <span class="token operator">==</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: true - 平等的</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">2</span> <span class="token operator">!=</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: true - 不相等</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">3</span> <span class="token operator">></span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: true - 比...更棒</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">2</span> <span class="token operator"><</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: true - 少于</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">3</span> <span class="token operator">>=</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: true - 大于或等于</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token number">2</span> <span class="token operator"><=</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: true - 小于或等于</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="运算符优先级示例"><a aria-hidden="true" tabindex="-1" href="#运算符优先级示例"><span class="icon icon-link"></span></a>运算符优先级示例</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 括号可以提高可读性。</span>
|
||
</span><span class="code-line"><span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>n <span class="token operator">%</span> i <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token operator">&&</span> <span class="token punctuation">(</span>d <span class="token operator">%</span> i <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
|
||
</span><span class="code-line"><span class="token comment">// 虽然难以阅读，但等效。</span>
|
||
</span><span class="code-line"><span class="token keyword">if</span> <span class="token punctuation">(</span>n <span class="token operator">%</span> i <span class="token operator">==</span> <span class="token number">0</span> <span class="token operator">&&</span> d <span class="token operator">%</span> i <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="位运算符和移位运算符"><a aria-hidden="true" tabindex="-1" href="#位运算符和移位运算符"><span class="icon icon-link"></span></a>位运算符和移位运算符</h3><div class="wrap-body">
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<table class="left-align"><thead><tr><th align="left">操作符</th><th>含义</th></tr></thead><tbody><tr><td align="left"><code>&</code></td><td>与（AND）</td></tr><tr><td align="left"><code>|</code></td><td>或（OR）</td></tr><tr><td align="left"><code>^</code></td><td>异或（XOR）</td></tr><tr><td align="left"><code>~expr</code></td><td>一元位补码<br><em>(0 变为 1；1 变为 0)</em></td></tr><tr><td align="left"><code><<</code></td><td>左移</td></tr><tr><td align="left"><code>>></code></td><td>右移</td></tr><tr><td align="left"><code>>>></code></td><td>无符号右移</td></tr></tbody></table>
|
||
<!--rehype:className=left-align-->
|
||
<hr>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">final</span> value <span class="token operator">=</span> <span class="token number">0x22</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">final</span> bitmask <span class="token operator">=</span> <span class="token number">0x0f</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token comment">// 与（AND）</span>
|
||
</span><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token punctuation">(</span>value <span class="token operator">&</span> bitmask<span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0x02</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 非与（AND NOT）</span>
|
||
</span><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token punctuation">(</span>value <span class="token operator">&</span> <span class="token operator">~</span>bitmask<span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0x20</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 或（OR）</span>
|
||
</span><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token punctuation">(</span>value <span class="token operator">|</span> bitmask<span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0x2f</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 异或（XOR）</span>
|
||
</span><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token punctuation">(</span>value <span class="token operator">^</span> bitmask<span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0x2d</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token punctuation">(</span>value <span class="token operator"><<</span> <span class="token number">4</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0x220</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 左移</span>
|
||
</span><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token punctuation">(</span>value <span class="token operator">>></span> <span class="token number">4</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0x02</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 右移</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="级联表示法"><a aria-hidden="true" tabindex="-1" href="#级联表示法"><span class="icon icon-link"></span></a>级联表示法</h3><div class="wrap-body">
|
||
<p>级联 (.., ?..) 允许您对同一对象进行一系列操作。除了访问实例成员之外，您还可以调用同一对象的实例方法。这通常可以节省您创建临时变量的步骤，并允许您编写更流畅的代码。考虑以下代码：</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">var</span> paint <span class="token operator">=</span> <span class="token class-name">Paint</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
</span><span class="code-line"> <span class="token punctuation">.</span><span class="token punctuation">.</span>color <span class="token operator">=</span> <span class="token class-name">Colors</span><span class="token punctuation">.</span>black
|
||
</span><span class="code-line"> <span class="token punctuation">.</span><span class="token punctuation">.</span>strokeCap <span class="token operator">=</span> <span class="token class-name">StrokeCap</span><span class="token punctuation">.</span>round
|
||
</span><span class="code-line"> <span class="token punctuation">.</span><span class="token punctuation">.</span>strokeWidth <span class="token operator">=</span> <span class="token number">5.0</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
<p>示例相当于以下代码：</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">var</span> paint <span class="token operator">=</span> <span class="token class-name">Paint</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">paint<span class="token punctuation">.</span>color <span class="token operator">=</span> <span class="token class-name">Colors</span><span class="token punctuation">.</span>black<span class="token punctuation">;</span>
|
||
</span><span class="code-line">paint<span class="token punctuation">.</span>strokeCap <span class="token operator">=</span> <span class="token class-name">StrokeCap</span><span class="token punctuation">.</span>round<span class="token punctuation">;</span>
|
||
</span><span class="code-line">paint<span class="token punctuation">.</span>strokeWidth <span class="token operator">=</span> <span class="token number">5.0</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
<p>以 <code>?...</code>开头可确保不会对该空对象进行任何级联操作。</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token function">querySelector</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'#confirm'</span></span><span class="token punctuation">)</span> <span class="token comment">// 获取一个对象</span>
|
||
</span><span class="code-line"> <span class="token operator">?</span><span class="token punctuation">.</span><span class="token punctuation">.</span>text <span class="token operator">=</span> <span class="token string-literal"><span class="token string">'Confirm'</span></span> <span class="token comment">// 使用它的成员</span>
|
||
</span><span class="code-line"> <span class="token punctuation">.</span><span class="token punctuation">.</span>classes<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'important'</span></span><span class="token punctuation">)</span>
|
||
</span><span class="code-line"> <span class="token punctuation">.</span><span class="token punctuation">.</span>onClick<span class="token punctuation">.</span><span class="token function">listen</span><span class="token punctuation">(</span><span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> window<span class="token punctuation">.</span><span class="token function">alert</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Confirmed!'</span></span><span class="token punctuation">)</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span><span class="token punctuation">)</span>
|
||
</span><span class="code-line"> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token function">scrollIntoView</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="控制流条件"><a aria-hidden="true" tabindex="-1" href="#控制流条件"><span class="icon icon-link"></span></a>控制流：条件</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist row-span-2"><div class="wrap-header h3wrap"><h3 id="if-和-else-if"><a aria-hidden="true" tabindex="-1" href="#if-和-else-if"><span class="icon icon-link"></span></a>if 和 else if</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">if</span><span class="token punctuation">(</span>age <span class="token operator"><</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Teen"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span><span class="token punctuation">(</span> age <span class="token operator">></span> <span class="token number">18</span> <span class="token operator">&&</span> age <span class="token operator"><</span><span class="token number">60</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Adult"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Old"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist row-span-2"><div class="wrap-header h3wrap"><h3 id="switch-case"><a aria-hidden="true" tabindex="-1" href="#switch-case"><span class="icon icon-link"></span></a>switch case</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">enum</span> <span class="token class-name">Pet</span> <span class="token punctuation">{</span>dog<span class="token punctuation">,</span> cat<span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token class-name">Pet</span> myPet <span class="token operator">=</span> <span class="token class-name">Pet</span><span class="token punctuation">.</span>dog<span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">switch</span><span class="token punctuation">(</span>myPet<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">case</span> <span class="token class-name">Pet</span><span class="token punctuation">.</span>dog<span class="token punctuation">:</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'My Pet is Dog.'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">break</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">case</span> <span class="token class-name">Pet</span><span class="token punctuation">.</span>cat<span class="token punctuation">:</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'My Pet is Cat.'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">break</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">default</span><span class="token punctuation">:</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'I don\'t have a Pet'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token comment">// 打印: My Pet is Dog.</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="三元操作符"><a aria-hidden="true" tabindex="-1" href="#三元操作符"><span class="icon icon-link"></span></a>三元操作符</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line">int age <span class="token operator">=</span> <span class="token number">20</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token class-name">String</span> message <span class="token operator">=</span> age <span class="token operator">>=</span> <span class="token number">18</span> <span class="token operator">?</span> <span class="token string-literal"><span class="token string">"成人"</span></span> <span class="token punctuation">:</span> <span class="token string-literal"><span class="token string">"儿童"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"年龄类别: </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">message</span></span><span class="token string">"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 输出: 年龄类别: 成人</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="三元操作符嵌套使用"><a aria-hidden="true" tabindex="-1" href="#三元操作符嵌套使用"><span class="icon icon-link"></span></a>三元操作符嵌套使用</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line">int x <span class="token operator">=</span> <span class="token number">10</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">int y <span class="token operator">=</span> <span class="token number">5</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">int result <span class="token operator">=</span> x <span class="token operator">></span> y <span class="token operator">?</span> x <span class="token punctuation">:</span> y <span class="token operator">></span> <span class="token number">0</span> <span class="token operator">?</span> y <span class="token punctuation">:</span> <span class="token number">0</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Result: </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">result</span></span><span class="token string">"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 输出: Result: 10</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="控制流循环"><a aria-hidden="true" tabindex="-1" href="#控制流循环"><span class="icon icon-link"></span></a>控制流：循环</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="while-循环"><a aria-hidden="true" tabindex="-1" href="#while-循环"><span class="icon icon-link"></span></a>while 循环</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token operator">!</span>dreamsAchieved<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">workHard</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
<p>循环迭代之前的 <code>while</code> 循环检查条件</p>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="do-while-循环"><a aria-hidden="true" tabindex="-1" href="#do-while-循环"><span class="icon icon-link"></span></a>do-while 循环</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">do</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">workHard</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span> <span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token operator">!</span>dreamsAchieved<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
<p><code>do-while</code> 循环在执行循环内的语句后验证条件</p>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="for-循环"><a aria-hidden="true" tabindex="-1" href="#for-循环"><span class="icon icon-link"></span></a>for 循环</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">for</span><span class="token punctuation">(</span>int i<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span> i<span class="token operator"><</span> <span class="token number">10</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> numbers <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 列表的 for-in 循环</span>
|
||
</span><span class="code-line"><span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">var</span> number <span class="token keyword">in</span> numbers<span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span>number<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="collections"><a aria-hidden="true" tabindex="-1" href="#collections"><span class="icon icon-link"></span></a>Collections</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="lists"><a aria-hidden="true" tabindex="-1" href="#lists"><span class="icon icon-link"></span></a>Lists</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 有序的对象组</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> list <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span>length<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//Print: 3</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span>list<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//Print: 2</span>
|
||
</span><span class="code-line"><span class="token comment">// 列表声明和初始化的其他方式</span>
|
||
</span><span class="code-line"><span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> cities <span class="token operator">=</span> <span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span><span class="token punctuation">[</span><span class="token string-literal"><span class="token string">"New York"</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">"Mumbai"</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">"Tokyo"</span></span><span class="token punctuation">]</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 创建一个编译时常量的列表</span>
|
||
</span><span class="code-line"><span class="token keyword">const</span> constantCities <span class="token operator">=</span> <span class="token keyword">const</span> <span class="token punctuation">[</span><span class="token string-literal"><span class="token string">"New York"</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">"Mumbai"</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">"Tokyo"</span></span><span class="token punctuation">]</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist row-span-2"><div class="wrap-header h3wrap"><h3 id="maps"><a aria-hidden="true" tabindex="-1" href="#maps"><span class="icon icon-link"></span></a>Maps</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 映射是关联键和值的对象</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> person <span class="token operator">=</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">String</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 要初始化映射，请执行以下操作：</span>
|
||
</span><span class="code-line">person<span class="token punctuation">[</span><span class="token string-literal"><span class="token string">'firstName'</span></span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token string-literal"><span class="token string">'Nicola'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">person<span class="token punctuation">[</span><span class="token string-literal"><span class="token string">'lastName'</span></span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token string-literal"><span class="token string">'Tesla'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span>person<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 打印: {firstName:Nicola, lastName:Tesla}</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span>person<span class="token punctuation">[</span><span class="token string-literal"><span class="token string">'lastName'</span></span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 打印: Tesla</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token keyword">var</span> nobleGases <span class="token operator">=</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// Key: Value</span>
|
||
</span><span class="code-line"> <span class="token number">2</span><span class="token punctuation">:</span> <span class="token string-literal"><span class="token string">'helium'</span></span><span class="token punctuation">,</span>
|
||
</span><span class="code-line"> <span class="token number">10</span><span class="token punctuation">:</span> <span class="token string-literal"><span class="token string">'neon'</span></span><span class="token punctuation">,</span>
|
||
</span><span class="code-line"> <span class="token number">18</span><span class="token punctuation">:</span> <span class="token string-literal"><span class="token string">'argon'</span></span><span class="token punctuation">,</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="sets"><a aria-hidden="true" tabindex="-1" href="#sets"><span class="icon icon-link"></span></a>Sets</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// Dart 中的集合是唯一项的无序集合</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> halogens <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token string-literal"><span class="token string">'fluorine'</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">'chlorine'</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">'bromine'</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">'iodine'</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">'astatine'</span></span><span class="token punctuation">}</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 创建一个空集</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> names <span class="token operator">=</span> <span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token class-name">Set</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> names <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span> <span class="token comment">// 这也有效</span>
|
||
</span><span class="code-line"><span class="token comment">//var names = {}; // 创建映射，而不是集合</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="函数"><a aria-hidden="true" tabindex="-1" href="#函数"><span class="icon icon-link"></span></a>函数</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="函数示例"><a aria-hidden="true" tabindex="-1" href="#函数示例"><span class="icon icon-link"></span></a>函数示例</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// dart 中的函数是对象并且有一个类型</span>
|
||
</span><span class="code-line">int <span class="token function">add</span><span class="token punctuation">(</span>int a<span class="token punctuation">,</span> int b<span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">return</span> a<span class="token operator">+</span>b<span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token comment">// 函数可以分配给变量</span>
|
||
</span><span class="code-line">int sum <span class="token operator">=</span> <span class="token function">add</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 回报：5</span>
|
||
</span><span class="code-line"><span class="token comment">// 可以作为参数传递给其他函数</span>
|
||
</span><span class="code-line">int totalSum <span class="token operator">=</span> <span class="token function">add</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token function">add</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 返回：7</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="箭头函数-"><a aria-hidden="true" tabindex="-1" href="#箭头函数-"><span class="icon icon-link"></span></a>箭头函数 (=>)</h3><div class="wrap-body">
|
||
<pre class="wrap-text"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 只包含一个表达式的函数，您可以使用简写语法</span>
|
||
</span><span class="code-line">bool <span class="token function">isFav</span><span class="token punctuation">(</span><span class="token class-name">Product</span> product<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span> favProductsList<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span>product<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
<!--rehype:className=wrap-text-->
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="anonymous-lambda-functions"><a aria-hidden="true" tabindex="-1" href="#anonymous-lambda-functions"><span class="icon icon-link"></span></a>Anonymous (lambda) functions</h3><div class="wrap-body">
|
||
<pre class="wrap-text"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 没有名字的小单行函数</span>
|
||
</span><span class="code-line">int <span class="token function">add</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span>b<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span> a<span class="token operator">+</span>b<span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// lambda 函数大多作为参数传递给其他函数</span>
|
||
</span><span class="code-line"><span class="token keyword">const</span> list <span class="token operator">=</span> <span class="token punctuation">[</span>
|
||
</span><span class="code-line"> <span class="token string-literal"><span class="token string">'apples'</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">'bananas'</span></span><span class="token punctuation">,</span> <span class="token string-literal"><span class="token string">'oranges'</span></span>
|
||
</span><span class="code-line"><span class="token punctuation">]</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line">list<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span>
|
||
</span><span class="code-line"> <span class="token punctuation">(</span>item<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'</span><span class="token interpolation"><span class="token punctuation">${</span><span class="token expression">list<span class="token punctuation">.</span><span class="token function">indexOf</span><span class="token punctuation">(</span>item<span class="token punctuation">)</span></span><span class="token punctuation">}</span></span><span class="token string">: </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">item</span></span><span class="token string">'</span></span><span class="token punctuation">)</span>
|
||
</span><span class="code-line"><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 打印: 0: apples 1: bananas 2: oranges</span>
|
||
</span></code></pre>
|
||
<!--rehype:className=wrap-text-->
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="扩展函数-extension"><a aria-hidden="true" tabindex="-1" href="#扩展函数-extension"><span class="icon icon-link"></span></a>扩展函数 (Extension)</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">//extension 定义扩展名称 on 扩展类</span>
|
||
</span><span class="code-line"><span class="token keyword">extension</span> <span class="token class-name">StringExtension</span> <span class="token keyword">on</span> <span class="token class-name">String</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">//扩展方法</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> <span class="token function">capitalize</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">if</span> <span class="token punctuation">(</span>isEmpty<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"> <span class="token comment">// 将字符串的首字母大写</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> topStr <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">toUpperCase</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"> <span class="token keyword">return</span> <span class="token string-literal"><span class="token string">'</span><span class="token interpolation"><span class="token punctuation">${</span><span class="token expression">topStr</span><span class="token punctuation">}</span></span><span class="token interpolation"><span class="token punctuation">${</span><span class="token expression"><span class="token function">substring</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span></span><span class="token punctuation">}</span></span><span class="token string">'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"apple"</span></span><span class="token punctuation">.</span><span class="token function">capitalize</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">// Print: Apple</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"苹果apple"</span></span><span class="token punctuation">.</span><span class="token function">capitalize</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">// Print: 苹果apple</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line">
|
||
</span></code></pre>
|
||
<p class="wrap-text">在不修改 String 类的前提下为其新增了 capitalize 方法</p>
|
||
<!--rehype:className=wrap-text-->
|
||
</div></div></div><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="运算符重载-extension"><a aria-hidden="true" tabindex="-1" href="#运算符重载-extension"><span class="icon icon-link"></span></a>运算符重载 (Extension)</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Money</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">final</span> num amount<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token class-name">Money</span><span class="token punctuation">(</span><span class="token punctuation">{</span>required <span class="token keyword">this</span><span class="token punctuation">.</span>amount<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token comment">// 利用扩展函数特性 </span>
|
||
</span><span class="code-line"><span class="token keyword">extension</span> <span class="token class-name">MoneyOperatorExtension</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">T</span><span class="token punctuation">></span></span> <span class="token keyword">on</span> <span class="token class-name">Money</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// operator 重载运算符</span>
|
||
</span><span class="code-line"> <span class="token class-name">Money</span> <span class="token keyword">operator</span> <span class="token operator">+</span><span class="token punctuation">(</span><span class="token class-name">Money</span> elements<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token class-name">Money</span> newMoney <span class="token operator">=</span> <span class="token class-name">Money</span><span class="token punctuation">(</span>amount<span class="token punctuation">:</span> <span class="token keyword">this</span><span class="token punctuation">.</span>amount <span class="token operator">+</span> elements<span class="token punctuation">.</span>amount<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">return</span> newMoney<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// 怎么样？两个类加起来了</span>
|
||
</span><span class="code-line"> <span class="token class-name">Money</span> appleMoney <span class="token operator">=</span> <span class="token class-name">Money</span><span class="token punctuation">(</span>amount<span class="token punctuation">:</span> <span class="token number">10.0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token class-name">Money</span> cardMoney <span class="token operator">=</span> <span class="token class-name">Money</span><span class="token punctuation">(</span>amount<span class="token punctuation">:</span> <span class="token number">6.0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token class-name">Money</span> allMoney <span class="token operator">=</span> cardMoney <span class="token operator">+</span> appleMoney<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span>allMoney<span class="token punctuation">.</span>amount<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">//Print: 16.0</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line">
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="类和对象"><a aria-hidden="true" tabindex="-1" href="#类和对象"><span class="icon icon-link"></span></a>类和对象</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="类-class"><a aria-hidden="true" tabindex="-1" href="#类-class"><span class="icon icon-link"></span></a>类 Class</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Cat</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">// 方法</span>
|
||
</span><span class="code-line"> <span class="token keyword">void</span> <span class="token function">voice</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Meow"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="对象-object"><a aria-hidden="true" tabindex="-1" href="#对象-object"><span class="icon icon-link"></span></a>对象 Object</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 类的实例</span>
|
||
</span><span class="code-line"><span class="token comment">// 在 myCat 下面是 Cat 类的对象</span>
|
||
</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token class-name">Cat</span> myCat <span class="token operator">=</span> <span class="token class-name">Cat</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> myCat<span class="token punctuation">.</span>name <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"Kitty"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> myCat<span class="token punctuation">.</span><span class="token function">voice</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: Meow</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="构造函数"><a aria-hidden="true" tabindex="-1" href="#构造函数"><span class="icon icon-link"></span></a>构造函数</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Cat</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token class-name">Cat</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>name<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token class-name">Cat</span> myCat <span class="token operator">=</span> <span class="token class-name">Cat</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Kitty"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span>myCat<span class="token punctuation">.</span>name<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: Kitty</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="抽象类"><a aria-hidden="true" tabindex="-1" href="#抽象类"><span class="icon icon-link"></span></a>抽象类</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 抽象类——不能实例化的类</span>
|
||
</span><span class="code-line"><span class="token comment">// 这个类被声明为抽象的，因此不能被实例化</span>
|
||
</span><span class="code-line"><span class="token keyword">abstract</span> <span class="token keyword">class</span> <span class="token class-name">AbstractContainer</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// 定义构造函数、字段、方法...</span>
|
||
</span><span class="code-line"> <span class="token keyword">void</span> <span class="token function">updateChildren</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 抽象方法</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="getters-setters"><a aria-hidden="true" tabindex="-1" href="#getters-setters"><span class="icon icon-link"></span></a>Getters Setters</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 提供对对象属性的读写访问</span>
|
||
</span><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Cat</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">// getter</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> <span class="token keyword">get</span> catName <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">return</span> name<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"> <span class="token comment">// setter</span>
|
||
</span><span class="code-line"> <span class="token keyword">void</span> <span class="token keyword">set</span> <span class="token function">catName</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="隐式接口"><a aria-hidden="true" tabindex="-1" href="#隐式接口"><span class="icon icon-link"></span></a>隐式接口</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="一个基本的界面"><a aria-hidden="true" tabindex="-1" href="#一个基本的界面"><span class="icon icon-link"></span></a>一个基本的界面</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 一个人。隐式接口包含 greet()。</span>
|
||
</span><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// 在接口中，但仅在此库中可见。</span>
|
||
</span><span class="code-line"> <span class="token keyword">final</span> <span class="token class-name">String</span> _name<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">// 不在接口中，因为这是一个构造函数。</span>
|
||
</span><span class="code-line"> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>_name<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">// 在接口中</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> <span class="token function">greet</span><span class="token punctuation">(</span><span class="token class-name">String</span> who<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span> <span class="token string-literal"><span class="token string">'Hello, </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">who</span></span><span class="token string">. I am </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">_name</span></span><span class="token string">.'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token comment">// Person 接口的实现。</span>
|
||
</span><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Impostor</span> <span class="token keyword">implements</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> <span class="token keyword">get</span> _name <span class="token operator">=</span><span class="token operator">></span> <span class="token string-literal"><span class="token string">''</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> <span class="token function">greet</span><span class="token punctuation">(</span><span class="token class-name">String</span> who<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span> <span class="token string-literal"><span class="token string">'Hi </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">who</span></span><span class="token string">. Do you know who I am?'</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token class-name">String</span> <span class="token function">greetBob</span><span class="token punctuation">(</span><span class="token class-name">Person</span> person<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span> person<span class="token punctuation">.</span><span class="token function">greet</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Bob'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token function">greetBob</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Kathy'</span></span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">// 打印: Hello, Bob. I am Kathy.</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token function">greetBob</span><span class="token punctuation">(</span><span class="token class-name">Impostor</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">// 打印: Hi Bob. Do you know who I am?</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="扩展类"><a aria-hidden="true" tabindex="-1" href="#扩展类"><span class="icon icon-link"></span></a>扩展类</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Phone</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">void</span> <span class="token function">use</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">_call</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token function">_sendMessage</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token comment">// 使用 extends 创建子类</span>
|
||
</span><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">SmartPhone</span> <span class="token keyword">extends</span> <span class="token class-name">Phone</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">void</span> <span class="token function">use</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// 使用 super 来引用超类</span>
|
||
</span><span class="code-line"> <span class="token keyword">super</span><span class="token punctuation">.</span><span class="token function">use</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token function">_takePhotos</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token function">_playGames</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="枚举"><a aria-hidden="true" tabindex="-1" href="#枚举"><span class="icon icon-link"></span></a>枚举</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="定义枚举"><a aria-hidden="true" tabindex="-1" href="#定义枚举"><span class="icon icon-link"></span></a>定义枚举</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">enum</span> <span class="token class-name">Color</span> <span class="token punctuation">{</span> red<span class="token punctuation">,</span> green<span class="token punctuation">,</span> blue <span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
<p>使用枚举，像访问任何其他静态变量一样访问枚举值：</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">final</span> favoriteColor <span class="token operator">=</span> <span class="token class-name">Color</span><span class="token punctuation">.</span>blue<span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">if</span> <span class="token punctuation">(</span>favoriteColor <span class="token operator">==</span> <span class="token class-name">Color</span><span class="token punctuation">.</span>blue<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Your favorite color is blue!'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
<p>枚举中的每个值都有一个索引获取器，它返回枚举声明中值从零开始的位置。 例如，第一个值的索引为 0，第二个值的索引为 1</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token class-name">Color</span><span class="token punctuation">.</span>red<span class="token punctuation">.</span>index <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token class-name">Color</span><span class="token punctuation">.</span>green<span class="token punctuation">.</span>index <span class="token operator">==</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span><span class="token class-name">Color</span><span class="token punctuation">.</span>blue<span class="token punctuation">.</span>index <span class="token operator">==</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
<p>要获取所有枚举值的列表，请使用枚举的值常量</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Color</span><span class="token punctuation">></span></span> colors <span class="token operator">=</span> <span class="token class-name">Color</span><span class="token punctuation">.</span>values<span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">assert</span><span class="token punctuation">(</span>colors<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span> <span class="token operator">==</span> <span class="token class-name">Color</span><span class="token punctuation">.</span>blue<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
<p>您可以在 switch 语句中使用枚举，如果您没有处理枚举的所有值，您将收到警告：</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">var</span> aColor <span class="token operator">=</span> <span class="token class-name">Color</span><span class="token punctuation">.</span>blue<span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token keyword">switch</span> <span class="token punctuation">(</span>aColor<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">case</span> <span class="token class-name">Color</span><span class="token punctuation">.</span>red<span class="token punctuation">:</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Red as roses!'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">break</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">case</span> <span class="token class-name">Color</span><span class="token punctuation">.</span>green<span class="token punctuation">:</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Green as grass!'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">break</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">default</span><span class="token punctuation">:</span> <span class="token comment">// 没有这个，你会看到一个警告</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span>aColor<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 'Color.blue'</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
<p>如果您需要访问枚举值的名称，例如 <code>Color.blue</code> 中的“blue”，请使用 <code>.name</code> 属性：</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token class-name">Color</span><span class="token punctuation">.</span>blue<span class="token punctuation">.</span>name<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 'blue'</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="枚举示例"><a aria-hidden="true" tabindex="-1" href="#枚举示例"><span class="icon icon-link"></span></a>枚举示例</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2-->
|
||
<p>声明了一个具有多个实例、实例变量、一个 <code>getter</code> 和一个已实现接口的增强型枚举</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 简单定义一个枚举类型</span>
|
||
</span><span class="code-line"><span class="token keyword">enum</span> <span class="token class-name">PlanetType</span> <span class="token punctuation">{</span> terrestrial<span class="token punctuation">,</span> gas<span class="token punctuation">,</span> ice <span class="token punctuation">}</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token comment">// 定义一个行星复杂的枚举类型</span>
|
||
</span><span class="code-line"><span class="token keyword">enum</span> <span class="token class-name">Planet</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">mercury</span><span class="token punctuation">(</span>planetType<span class="token punctuation">:</span> <span class="token class-name">PlanetType</span><span class="token punctuation">.</span>terrestrial<span class="token punctuation">,</span> moons<span class="token punctuation">:</span> <span class="token number">0</span><span class="token punctuation">,</span> hasRings<span class="token punctuation">:</span> <span class="token boolean">false</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||
</span><span class="code-line"> <span class="token function">venus</span><span class="token punctuation">(</span>planetType<span class="token punctuation">:</span> <span class="token class-name">PlanetType</span><span class="token punctuation">.</span>terrestrial<span class="token punctuation">,</span> moons<span class="token punctuation">:</span> <span class="token number">0</span><span class="token punctuation">,</span> hasRings<span class="token punctuation">:</span> <span class="token boolean">false</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"> <span class="token function">uranus</span><span class="token punctuation">(</span>planetType<span class="token punctuation">:</span> <span class="token class-name">PlanetType</span><span class="token punctuation">.</span>ice<span class="token punctuation">,</span> moons<span class="token punctuation">:</span> <span class="token number">27</span><span class="token punctuation">,</span> hasRings<span class="token punctuation">:</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||
</span><span class="code-line"> <span class="token function">neptune</span><span class="token punctuation">(</span>planetType<span class="token punctuation">:</span> <span class="token class-name">PlanetType</span><span class="token punctuation">.</span>ice<span class="token punctuation">,</span> moons<span class="token punctuation">:</span> <span class="token number">14</span><span class="token punctuation">,</span> hasRings<span class="token punctuation">:</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"> <span class="token comment">// 定义一个构造函数</span>
|
||
</span><span class="code-line"> <span class="token keyword">const</span> <span class="token class-name">Planet</span><span class="token punctuation">(</span><span class="token punctuation">{</span>required <span class="token keyword">this</span><span class="token punctuation">.</span>planetType<span class="token punctuation">,</span> required <span class="token keyword">this</span><span class="token punctuation">.</span>moons<span class="token punctuation">,</span> required <span class="token keyword">this</span><span class="token punctuation">.</span>hasRings<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"> <span class="token comment">// 声明枚举类型中的变量</span>
|
||
</span><span class="code-line"> <span class="token keyword">final</span> <span class="token class-name">PlanetType</span> planetType<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">final</span> int moons<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">final</span> bool hasRings<span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"> <span class="token comment">// 实现枚举类型中的get 方法</span>
|
||
</span><span class="code-line"> bool <span class="token keyword">get</span> isGiant <span class="token operator">=</span><span class="token operator">></span>
|
||
</span><span class="code-line"> planetType <span class="token operator">==</span> <span class="token class-name">PlanetType</span><span class="token punctuation">.</span>gas <span class="token operator">||</span> planetType <span class="token operator">==</span> <span class="token class-name">PlanetType</span><span class="token punctuation">.</span>ice<span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token comment">// 使用枚举类型</span>
|
||
</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
</span><span class="code-line"><span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">final</span> yourPlanet <span class="token operator">=</span> <span class="token class-name">Planet</span><span class="token punctuation">.</span>mercury<span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>yourPlanet<span class="token punctuation">.</span>isGiant<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Your planet is not a "giant planet".'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="mixin"><a aria-hidden="true" tabindex="-1" href="#mixin"><span class="icon icon-link"></span></a>Mixin</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="定义mixin"><a aria-hidden="true" tabindex="-1" href="#定义mixin"><span class="icon icon-link"></span></a>定义Mixin</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2-->
|
||
<p><code>Dart</code>中类只能单继承，使用<code>Mixin</code>可以实现多个继承，复用多个类中代码的方法。</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 定义Mixin</span>
|
||
</span><span class="code-line"><span class="token keyword">mixin</span> <span class="token class-name">Piloted</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> int astronauts <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"> <span class="token keyword">void</span> <span class="token function">describeCrew</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Number of astronauts: </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">astronauts</span></span><span class="token string">'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
<p>使用<code>with</code>关键字并在其后跟上<code>Mixin类</code>的名字来使用</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 使用with将Piloted混入</span>
|
||
</span><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">PilotedCraft</span> <span class="token keyword">extends</span> <span class="token class-name">Spacecraft</span> <span class="token keyword">with</span> <span class="token class-name">Piloted</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// ···</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
<p>支持混入多个Mixin，如果出现相同的方法后混入的Mixin会覆盖前面的</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Musician</span> <span class="token keyword">extends</span> <span class="token class-name">Performer</span> <span class="token keyword">with</span> <span class="token class-name">Musical</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// ···</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token comment">// 混入多个Mixin</span>
|
||
</span><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Maestro</span> <span class="token keyword">extends</span> <span class="token class-name">Person</span> <span class="token keyword">with</span> <span class="token class-name">Musical</span><span class="token punctuation">,</span> <span class="token class-name">Aggressive</span><span class="token punctuation">,</span> <span class="token class-name">Demented</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token class-name">Maestro</span><span class="token punctuation">(</span><span class="token class-name">String</span> maestroName<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> name <span class="token operator">=</span> maestroName<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> canConduct <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
<p>使用关键字<code>on</code>来指定哪些类可以使用该Mixin，比如有Mixin类<code>MusicalPerformer</code>，但是<code>MusicalPerformer</code>只能被<code>Musician</code>类使用，则可以这样定义<code>MusicalPerformer</code>：</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">Musician</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// ...</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token comment">// 现在MusicalPerformer 只能在 Musican及其子类中使用</span>
|
||
</span><span class="code-line"><span class="token keyword">mixin</span> <span class="token class-name">MusicalPerformer</span> <span class="token keyword">on</span> <span class="token class-name">Musician</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// ...</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token keyword">class</span> <span class="token class-name">SingerDancer</span> <span class="token keyword">extends</span> <span class="token class-name">Musician</span> <span class="token keyword">with</span> <span class="token class-name">MusicalPerformer</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// ...</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="异常"><a aria-hidden="true" tabindex="-1" href="#异常"><span class="icon icon-link"></span></a>异常</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="throw"><a aria-hidden="true" tabindex="-1" href="#throw"><span class="icon icon-link"></span></a>Throw</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 抛出 throws 或引发 raises 和异常 exception</span>
|
||
</span><span class="code-line"><span class="token keyword">throw</span> <span class="token class-name">IntegerDivisionByZeroException</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 你也可以抛出任意对象</span>
|
||
</span><span class="code-line"><span class="token keyword">throw</span> <span class="token string-literal"><span class="token string">"Product out of stock!"</span></span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="catch"><a aria-hidden="true" tabindex="-1" href="#catch"><span class="icon icon-link"></span></a>Catch</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token keyword">try</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> int c <span class="token operator">=</span> <span class="token number">3</span><span class="token operator">/</span><span class="token number">0</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span>c<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span> <span class="token keyword">on</span> <span class="token class-name">IntegerDivisionByZeroException</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// 一个特定的异常</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Can not divide integer by 0.'</span></span><span class="token punctuation">)</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span> <span class="token keyword">on</span> <span class="token class-name">Exception</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// 任何其他异常情况</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Unknown exception: </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">e</span></span><span class="token string">'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// 没有指定类型，处理所有</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Something really unknown: </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">e</span></span><span class="token string">'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="finally"><a aria-hidden="true" tabindex="-1" href="#finally"><span class="icon icon-link"></span></a>Finally</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 确保某些代码无论是否抛出异常都能运行</span>
|
||
</span><span class="code-line"><span class="token keyword">try</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">cookFood</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span>e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Error: </span><span class="token interpolation"><span class="token punctuation">$</span><span class="token expression">e</span></span><span class="token string">'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 先处理异常</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">cleanKitchen</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 然后清理</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="futures"><a aria-hidden="true" tabindex="-1" href="#futures"><span class="icon icon-link"></span></a>Futures</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="async-await"><a aria-hidden="true" tabindex="-1" href="#async-await"><span class="icon icon-link"></span></a>Async Await</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 异步函数：它们在设置可能耗时的操作后返回</span>
|
||
</span><span class="code-line"><span class="token comment">// async 和 await 关键字支持异步编程</span>
|
||
</span><span class="code-line"><span class="token class-name">Future</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> <span class="token function">login</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> userName<span class="token operator">=</span><span class="token string-literal"><span class="token string">"Temidjoy"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">return</span>
|
||
</span><span class="code-line"> <span class="token class-name">Future</span><span class="token punctuation">.</span><span class="token function">delayed</span><span class="token punctuation">(</span>
|
||
</span><span class="code-line"> <span class="token class-name">Duration</span><span class="token punctuation">(</span>seconds<span class="token punctuation">:</span> <span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span> userName
|
||
</span><span class="code-line"> <span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token comment">// 异步</span>
|
||
</span><span class="code-line"><span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">async</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Authenticating please wait...'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token class-name">String</span> result <span class="token operator">=</span> <span class="token keyword">await</span> <span class="token function">login</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span>result<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="各种各样的"><a aria-hidden="true" tabindex="-1" href="#各种各样的"><span class="icon icon-link"></span></a>各种各样的</h2><div class="wrap-body">
|
||
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="null-和-null-感知"><a aria-hidden="true" tabindex="-1" href="#null-和-null-感知"><span class="icon icon-link"></span></a>Null 和 Null 感知</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line">int x<span class="token punctuation">;</span> <span class="token comment">// 任何对象的初始值为 null</span>
|
||
</span><span class="code-line"><span class="token comment">// ?? 空感知运算符</span>
|
||
</span><span class="code-line">x <span class="token operator">?</span><span class="token operator">?</span><span class="token operator">=</span><span class="token number">6</span><span class="token punctuation">;</span> <span class="token comment">// ??= 赋值运算符，仅当变量当前为 null 时才为其赋值</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 6</span>
|
||
</span><span class="code-line">x <span class="token operator">?</span><span class="token operator">?</span><span class="token operator">=</span><span class="token number">3</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 6 - 结果仍然是 6</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span><span class="token keyword">null</span> <span class="token operator">?</span><span class="token operator">?</span> <span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 10。如果不为空，则显示左侧的值，否则返回右侧的值</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="三元运算符"><a aria-hidden="true" tabindex="-1" href="#三元运算符"><span class="icon icon-link"></span></a>三元运算符</h3><div class="wrap-body">
|
||
<pre class="wrap-text"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 条件 ? 条件如果为真 : 条件如果为假</span>
|
||
</span><span class="code-line">bool isAvailable<span class="token punctuation">;</span>
|
||
</span><span class="code-line">isAvailable <span class="token operator">?</span> <span class="token function">orderproduct</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">:</span> <span class="token function">addToFavourite</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
<!--rehype:className=wrap-text-->
|
||
</div></div></div><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="条件属性访问"><a aria-hidden="true" tabindex="-1" href="#条件属性访问"><span class="icon icon-link"></span></a>条件属性访问</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2-->
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line">userObject<span class="token operator">?</span><span class="token punctuation">.</span>userName
|
||
</span><span class="code-line"><span class="token comment">// 上面的代码片段等效于以下代码：</span>
|
||
</span><span class="code-line"><span class="token punctuation">(</span>userObject <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token operator">?</span> userObject<span class="token punctuation">.</span>userName <span class="token punctuation">:</span> <span class="token keyword">null</span>
|
||
</span><span class="code-line"><span class="token comment">// 您可以将 ? 的多种用途链接起来。一起在一个表达式中</span>
|
||
</span><span class="code-line">userObject<span class="token operator">?</span><span class="token punctuation">.</span>userName<span class="token operator">?</span><span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
</span><span class="code-line"><span class="token comment">// 如果 userObject 或 userObject.userName 为 null，则前面的代码返回 null 并且从不调用 toString()</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="扩展运算符-"><a aria-hidden="true" tabindex="-1" href="#扩展运算符-"><span class="icon icon-link"></span></a>扩展运算符 (...)</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 将多个值插入到集合中</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> list <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> list2 <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>list<span class="token punctuation">]</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token function">print</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span>length<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 打印: 4</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist col-span-2 row-span-2"><div class="wrap-header h3wrap"><h3 id="enum"><a aria-hidden="true" tabindex="-1" href="#enum"><span class="icon icon-link"></span></a>enum</h3><div class="wrap-body">
|
||
<!--rehype:wrap-class=col-span-2 row-span-2-->
|
||
<p>定义：enum（"enumeration"的缩写）是一种特殊的数据类型，可使变量成为一组预定义的常量。枚举用于定义只能从一小组可能值中选择一个的变量。通过为这些值集提供有意义的名称，枚举有助于提高代码的可读性，减少出错率。</p>
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 定义枚举类型</span>
|
||
</span><span class="code-line"><span class="token keyword">enum</span> <span class="token class-name">TrafficLight</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> red<span class="token punctuation">,</span>
|
||
</span><span class="code-line"> yellow<span class="token punctuation">,</span>
|
||
</span><span class="code-line"> green
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token comment">// 根据交通灯状态打印消息的函数</span>
|
||
</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">printTrafficLightMessage</span><span class="token punctuation">(</span><span class="token class-name">TrafficLight</span> light<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">switch</span> <span class="token punctuation">(</span>light<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token keyword">case</span> <span class="token class-name">TrafficLight</span><span class="token punctuation">.</span>red<span class="token punctuation">:</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Stop!'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">break</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">case</span> <span class="token class-name">TrafficLight</span><span class="token punctuation">.</span>yellow<span class="token punctuation">:</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Get ready...'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">break</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">case</span> <span class="token class-name">TrafficLight</span><span class="token punctuation">.</span>green<span class="token punctuation">:</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">'Go!'</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token keyword">break</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">// 枚举类型的示例用法</span>
|
||
</span><span class="code-line"> <span class="token class-name">TrafficLight</span> currentLight <span class="token operator">=</span> <span class="token class-name">TrafficLight</span><span class="token punctuation">.</span>green<span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token comment">// 打印当前交通灯状态的消息</span>
|
||
</span><span class="code-line"> <span class="token function">printTrafficLightMessage</span><span class="token punctuation">(</span>currentLight<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="级联符号-"><a aria-hidden="true" tabindex="-1" href="#级联符号-"><span class="icon icon-link"></span></a>级联符号 (..)</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// 允许您对同一对象进行一系列操作</span>
|
||
</span><span class="code-line"><span class="token comment">// 而不是这样做</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> user <span class="token operator">=</span> <span class="token class-name">User</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">user<span class="token punctuation">.</span>name <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"Nicola"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">user<span class="token punctuation">.</span>email <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"nicola@g.c"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line">user<span class="token punctuation">.</span>age <span class="token operator">=</span> <span class="token number">24</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token comment">// 你可以这样做</span>
|
||
</span><span class="code-line"><span class="token keyword">var</span> user <span class="token operator">=</span> <span class="token class-name">User</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
</span><span class="code-line"> <span class="token punctuation">.</span><span class="token punctuation">.</span>name <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"Nicola"</span></span>
|
||
</span><span class="code-line"> <span class="token punctuation">.</span><span class="token punctuation">.</span>email <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"nicola@g.c"</span></span>
|
||
</span><span class="code-line"> <span class="token punctuation">.</span><span class="token punctuation">.</span>age <span class="token operator">=</span> <span class="token number">24</span><span class="token punctuation">;</span>
|
||
</span></code></pre>
|
||
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="延迟初始化"><a aria-hidden="true" tabindex="-1" href="#延迟初始化"><span class="icon icon-link"></span></a>延迟初始化</h3><div class="wrap-body">
|
||
<pre class="language-dart"><code class="language-dart code-highlight"><span class="code-line"><span class="token comment">// token 类型非空，但是不用立即赋值</span>
|
||
</span><span class="code-line">late <span class="token class-name">String</span> token<span class="token punctuation">;</span>
|
||
</span><span class="code-line">
|
||
</span><span class="code-line"><span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
||
</span><span class="code-line"> <span class="token comment">/// print(token);</span>
|
||
</span><span class="code-line"> <span class="token comment">/// 字段 "token "尚未初始化</span>
|
||
</span><span class="code-line"> <span class="token comment">/// 在初始化前调用就会报错</span>
|
||
</span><span class="code-line"> token <span class="token operator">=</span> <span class="token string-literal"><span class="token string">"tokenContent"</span></span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"> <span class="token function">print</span><span class="token punctuation">(</span>token<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||
</span><span class="code-line"><span class="token punctuation">}</span>
|
||
</span></code></pre>
|
||
</div></div></div></div></div><div class="wrap h2body-not-exist"><div class="wrap-header h2wrap"><h2 id="另见"><a aria-hidden="true" tabindex="-1" href="#另见"><span class="icon icon-link"></span></a>另见</h2><div class="wrap-body">
|
||
<ul>
|
||
<li><a href="https://dart.dev/">Dart 官方文档</a> <em>(dart.dev)</em></li>
|
||
<li><a href="https://dart.cn/">Dart 中文社区官方文档</a> <em>(dart.cn)</em></li>
|
||
</ul>
|
||
</div></div><div class="h2wrap-body"></div></div></div><script src="https://giscus.app/client.js" data-repo="jaywcjlove/reference" data-repo-id="R_kgDOID2-Mw" data-category="Q&A" data-category-id="DIC_kwDOID2-M84CS5wo" data-mapping="pathname" data-strict="0" data-reactions-enabled="1" data-emit-metadata="0" data-input-position="bottom" data-theme="dark" data-lang="zh-CN" crossorigin="anonymous" async></script><div class="giscus"></div></div><footer class="footer-wrap"><footer class="max-container">© 2022 <a href="https://wangchujiang.com/#/app" target="_blank">Kenny Wang</a>.</footer></footer><script src="../data.js?v=1.8.3" defer></script><script src="../js/fuse.min.js?v=1.8.3" defer></script><script src="../js/main.js?v=1.8.3" defer></script><div id="mysearch"><div class="mysearch-box"><div class="mysearch-input"><div><svg xmlns="http://www.w3.org/2000/svg" height="1em" width="1em" viewBox="0 0 18 18">
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