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<title>Keyed Fragments | React</title>
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<a href="/react/tips/introduction.html">Introduction</a>
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<a href="/react/tips/children-props-type.html">Type of the Children props</a>
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<a href="/react/tips/props-in-getInitialState-as-anti-pattern.html">Props in getInitialState Is an Anti-Pattern</a>
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<a href="/react/tips/dom-event-listeners.html">DOM Event Listeners in a Component</a>
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<a href="/react/tips/false-in-jsx.html">False in JSX</a>
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<a href="/react/tips/expose-component-functions.html">Expose Component Functions</a>
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<a href="/react/tips/children-undefined.html">this.props.children undefined</a>
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<a href="/react/tips/use-react-with-other-libraries.html">Use React with Other Libraries</a>
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<a href="/react/tips/dangerously-set-inner-html.html">Dangerously Set innerHTML</a>
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</div>
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</div>
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<div class="inner-content">
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<h1>
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Keyed Fragments
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<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/10.6-create-fragment.zh-CN.md" target="_blank">Edit on GitHub</a>
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</h1>
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<div class="subHeader"></div>
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<p>在大多数情况下，你可以使用 <code>key</code> prop 指定你从 <code>render</code> 返回的元素的 keys。然而，这在一个情况下会失败：如果你有两组你需要记录的子级，将没有办法在不使用包裹元素的情况下放置一个 key 到每组上。</p>
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<p>即是，如果你有一个像这样的组件：</p>
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<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">var</span> <span class="nx">Swapper</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
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<span class="nx">propTypes</span><span class="o">:</span> <span class="p">{</span>
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<span class="c1">// `leftChildren` and `rightChildren` can be a string, element, array, etc.</span>
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<span class="nx">leftChildren</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">node</span><span class="p">,</span>
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<span class="nx">rightChildren</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">node</span><span class="p">,</span>
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<span class="nx">swapped</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">bool</span>
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<span class="p">},</span>
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<span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
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<span class="kd">var</span> <span class="nx">children</span><span class="p">;</span>
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<span class="k">if</span> <span class="p">(</span><span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">swapped</span><span class="p">)</span> <span class="p">{</span>
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<span class="nx">children</span> <span class="o">=</span> <span class="p">[</span><span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">rightChildren</span><span class="p">,</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">leftChildren</span><span class="p">];</span>
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<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
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<span class="nx">children</span> <span class="o">=</span> <span class="p">[</span><span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">leftChildren</span><span class="p">,</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">rightChildren</span><span class="p">];</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="o"><</span><span class="nx">div</span><span class="o">></span><span class="p">{</span><span class="nx">children</span><span class="p">}</span><span class="o"><</span><span class="err">/div>;</span>
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<span class="p">}</span>
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<span class="p">});</span>
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</code></pre></div>
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<p>这些子级会在当你改变 <code>swapped</code> prop 时加载和卸载，因为没有任何的 key 标记在这两组子级上。</p>
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<p>要解决这个问题，你可以使用 <code>createFragment</code> 插件来给予这两组子级 keys.</p>
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<h4><a class="anchor" name="arrayltreactnodegt-createfragmentobject-children"></a><code>Array<ReactNode> createFragment(object children)</code> <a class="hash-link" href="#arrayltreactnodegt-createfragmentobject-children">#</a></h4>
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<p>代替创建数组，我们这样写：</p>
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<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">var</span> <span class="nx">createFragment</span> <span class="o">=</span> <span class="nx">require</span><span class="p">(</span><span class="s1">'react-addons-create-fragment'</span><span class="p">);</span>
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<span class="k">if</span> <span class="p">(</span><span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">swapped</span><span class="p">)</span> <span class="p">{</span>
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<span class="nx">children</span> <span class="o">=</span> <span class="nx">createFragment</span><span class="p">({</span>
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<span class="nx">right</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">rightChildren</span><span class="p">,</span>
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<span class="nx">left</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">leftChildren</span>
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<span class="p">});</span>
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<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
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<span class="nx">children</span> <span class="o">=</span> <span class="nx">createFragment</span><span class="p">({</span>
|
||
<span class="nx">left</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">leftChildren</span><span class="p">,</span>
|
||
<span class="nx">right</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">rightChildren</span>
|
||
<span class="p">});</span>
|
||
<span class="p">}</span>
|
||
</code></pre></div>
|
||
<p>被传入对象的 keys （即 <code>left</code> 和 <code>right</code>）被用作为整组子级的 keys，并且对象 keys 的顺序被用于决定渲染子级的顺序。通过这个改变，这两个子级将会恰当的在 DOM 里排序，而不被卸载。</p>
|
||
|
||
<p><code>createFragment</code> 的返回值应该被对待为一个不透明的对象;你可以使用 <code>React.Children</code> 来遍历一个 fragment 但是不应该直接访问它。同样注意，我们依赖于 JavaScript 引擎保留了对象的枚举顺序，这点在 spec 上是不保证的，但是所有主要的浏览器和 VMs 都对非数字键的对象实现了这个特性。</p>
|
||
|
||
<blockquote>
|
||
<p><strong>注意:</strong></p>
|
||
|
||
<p>将来，<code>createFragment</code> 也许会被替换为如下的API：</p>
|
||
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="k">return</span> <span class="p">(</span>
|
||
<span class="o"><</span><span class="nx">div</span><span class="o">></span>
|
||
<span class="o"><</span><span class="nx">x</span><span class="o">:</span><span class="nx">frag</span> <span class="nx">key</span><span class="o">=</span><span class="s2">"right"</span><span class="o">></span><span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">rightChildren</span><span class="p">}</span><span class="o"><</span><span class="err">/x:frag>,</span>
|
||
<span class="o"><</span><span class="nx">x</span><span class="o">:</span><span class="nx">frag</span> <span class="nx">key</span><span class="o">=</span><span class="s2">"left"</span><span class="o">></span><span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">leftChildren</span><span class="p">}</span><span class="o"><</span><span class="err">/x:frag></span>
|
||
<span class="o"><</span><span class="err">/div></span>
|
||
<span class="p">);</span>
|
||
</code></pre></div>
|
||
<p>允许你直接在 JSX 里赋值 keys 而不用添加包裹元素。 </p>
|
||
</blockquote>
|
||
|
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|
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