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Dan Abramov
658 lines
36 KiB
HTML
658 lines
36 KiB
HTML
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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/contributing/how-to-contribute.html">How to Contribute</a>
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<a href="/react/contributing/codebase-overview.html">Codebase Overview</a>
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<li>
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<a href="/react/contributing/design-principles.html">Design Principles</a>
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</ul>
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</div>
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</div>
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<div class="inner-content">
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<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/12-context.zh-CN.md" target="_blank">Edit on GitHub</a>
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<h1>
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Context
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</h1>
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<div class="subHeader"></div>
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<p>React优势之一是你可以很容易地从React组件里跟踪数据流动。当你查看一个组件时，你可以很容易地判断出传入了哪些props，而这也有利于你的App进行逻辑推断。</p>
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<p>有时，你想不通过在每一级组件设置prop的方式来向组件树内传递数据。那么，React的"context"特性可以让你做到这点。</p>
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<blockquote>
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<p>注意：</p>
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<p>Context是一个先进的实验性特性，这个API很可能在未来版本变化。</p>
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<p>大多数应用将不会需要用到context。尤其是如果你刚开始用React，你很可能不会想用它。使用context将会使你的代码难以理解，因为它让数据流变得不清晰。它类似于在你的应用里用以传递state的全局变量。</p>
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<p><strong>如果你必须使用context，请保守地使用它。</strong></p>
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<p>不论你正在创建一个应用或者是库，试着缩小context的使用范围，并尽可能避免直接使用context相关API，以便在API变动时容易升级。</p>
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</blockquote>
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<h2><a class="anchor" name="在组件树内自动传递info"></a>在组件树内自动传递info <a class="hash-link" href="#在组件树内自动传递info">#</a></h2>
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<p>假设你有一个这样的结构:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">Button</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">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="k">return</span> <span class="p">(</span>
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<span class="o"><</span><span class="nx">button</span> <span class="nx">style</span><span class="o">=</span><span class="p">{{</span><span class="nx">background</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">color</span><span class="p">}}</span><span class="o">></span>
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<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">children</span><span class="p">}</span>
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<span class="o"><</span><span class="err">/button></span>
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<span class="p">);</span>
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<span class="p">}</span>
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<span class="p">});</span>
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<span class="kd">var</span> <span class="nx">Message</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">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="k">return</span> <span class="p">(</span>
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<span class="o"><</span><span class="nx">div</span><span class="o">></span>
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<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">text</span><span class="p">}</span> <span class="o"><</span><span class="nx">Button</span> <span class="nx">color</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">color</span><span class="p">}</span><span class="o">></span><span class="nx">Delete</span><span class="o"><</span><span class="err">/Button></span>
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<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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<span class="p">});</span>
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<span class="kd">var</span> <span class="nx">MessageList</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">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">color</span> <span class="o">=</span> <span class="s2">"purple"</span><span class="p">;</span>
|
|
<span class="kd">var</span> <span class="nx">children</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">messages</span><span class="p">.</span><span class="nx">map</span><span class="p">(</span><span class="kd">function</span><span class="p">(</span><span class="nx">message</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="o"><</span><span class="nx">Message</span> <span class="nx">text</span><span class="o">=</span><span class="p">{</span><span class="nx">message</span><span class="p">.</span><span class="nx">text</span><span class="p">}</span> <span class="nx">color</span><span class="o">=</span><span class="p">{</span><span class="nx">color</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
|
|
<span class="p">});</span>
|
|
<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>
|
|
<span class="p">}</span>
|
|
<span class="p">});</span>
|
|
</code></pre></div>
|
|
<p>在这个例子里，我们手工传递一个叫<code>color</code>的prop，以便于给<code>Button</code>和<code>Message</code>组件添加合适的样式。当你想所有子组件可以访问一部分信息时(比如color)，上面的设置主题是一个很好的例子。通过使用context，我们能自动在组件树中传递信息：</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">Button</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
|
|
<span class="hll"> <span class="nx">contextTypes</span><span class="o">:</span> <span class="p">{</span>
|
|
</span><span class="hll"> <span class="nx">color</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">string</span>
|
|
</span><span class="hll"> <span class="p">},</span>
|
|
</span> <span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">(</span>
|
|
<span class="hll"> <span class="o"><</span><span class="nx">button</span> <span class="nx">style</span><span class="o">=</span><span class="p">{{</span><span class="nx">background</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">context</span><span class="p">.</span><span class="nx">color</span><span class="p">}}</span><span class="o">></span>
|
|
</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">children</span><span class="p">}</span>
|
|
<span class="o"><</span><span class="err">/button></span>
|
|
<span class="p">);</span>
|
|
<span class="p">}</span>
|
|
<span class="p">});</span>
|
|
|
|
<span class="kd">var</span> <span class="nx">Message</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
|
|
<span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">div</span><span class="o">></span>
|
|
<span class="hll"> <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">text</span><span class="p">}</span> <span class="o"><</span><span class="nx">Button</span><span class="o">></span><span class="nx">Delete</span><span class="o"><</span><span class="err">/Button></span>
|
|
</span> <span class="o"><</span><span class="err">/div></span>
|
|
<span class="p">);</span>
|
|
<span class="p">}</span>
|
|
<span class="p">});</span>
|
|
|
|
<span class="kd">var</span> <span class="nx">MessageList</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
|
|
<span class="hll"> <span class="nx">childContextTypes</span><span class="o">:</span> <span class="p">{</span>
|
|
</span><span class="hll"> <span class="nx">color</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">string</span>
|
|
</span><span class="hll"> <span class="p">},</span>
|
|
</span><span class="hll"> <span class="nx">getChildContext</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
|
|
</span><span class="hll"> <span class="k">return</span> <span class="p">{</span><span class="nx">color</span><span class="o">:</span> <span class="s2">"purple"</span><span class="p">};</span>
|
|
</span><span class="hll"> <span class="p">},</span>
|
|
</span> <span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="kd">var</span> <span class="nx">children</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">messages</span><span class="p">.</span><span class="nx">map</span><span class="p">(</span><span class="kd">function</span><span class="p">(</span><span class="nx">message</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="hll"> <span class="k">return</span> <span class="o"><</span><span class="nx">Message</span> <span class="nx">text</span><span class="o">=</span><span class="p">{</span><span class="nx">message</span><span class="p">.</span><span class="nx">text</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
|
|
</span> <span class="p">});</span>
|
|
<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>
|
|
<span class="p">}</span>
|
|
<span class="p">});</span>
|
|
</code></pre></div>
|
|
<p>通过添加<code>childContextTypes</code>和<code>getChildContext</code>到 <code>MessageList</code>(context提供者)，React会自动下传信息，并且通过定义<code>contextTypes</code>，子树中的任何组件(在这个例子中，子组件是<code>Button</code>)可以访问<code>context</code>。</p>
|
|
|
|
<p>如果<code>contextTypes</code>没有定义，那么<code>this.context</code>将是一个空对象。</p>
|
|
<h2><a class="anchor" name="父子耦合"></a>父子耦合 <a class="hash-link" href="#父子耦合">#</a></h2>
|
|
<p>Context同样可以使你构建这样的API:</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">Menu</span><span class="o">></span>
|
|
<span class="o"><</span><span class="nx">MenuItem</span><span class="o">></span><span class="nx">aubergine</span><span class="o"><</span><span class="err">/MenuItem></span>
|
|
<span class="o"><</span><span class="nx">MenuItem</span><span class="o">></span><span class="nx">butternut</span> <span class="nx">squash</span><span class="o"><</span><span class="err">/MenuItem></span>
|
|
<span class="o"><</span><span class="nx">MenuItem</span><span class="o">></span><span class="nx">clementine</span><span class="o"><</span><span class="err">/MenuItem></span>
|
|
<span class="o"><</span><span class="err">/Menu></span>
|
|
</code></pre></div>
|
|
<p>通过在<code>Menu</code>组件内下传相关的信息，每个<code>MenuItem</code> 可以与包含他们的<code>Menu</code>组件沟通。</p>
|
|
|
|
<p><strong>在你用这个API构建组件以前，考虑一下是否有清晰的替代方案</strong> 我们喜欢用数组传递items，就像下面这样：</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="o"><</span><span class="nx">Menu</span> <span class="nx">items</span><span class="o">=</span><span class="p">{[</span><span class="s1">'aubergine'</span><span class="p">,</span> <span class="s1">'butternut squash'</span><span class="p">,</span> <span class="s1">'clementine'</span><span class="p">]}</span> <span class="o">/></span>
|
|
</code></pre></div>
|
|
<p>记住，如果你愿意，你同样可以在props里传递整个React组件。</p>
|
|
<h2><a class="anchor" name="在生命周期方法里引用context"></a>在生命周期方法里引用context <a class="hash-link" href="#在生命周期方法里引用context">#</a></h2>
|
|
<p>如果<code>contextTypes</code>是定义在一个组件中，接下来的生命周期方法会收到一个额外的参数，<code>context</code>对象：</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">componentWillReceiveProps</span><span class="p">(</span>
|
|
<span class="nx">object</span> <span class="nx">nextProps</span><span class="p">,</span> <span class="nx">object</span> <span class="nx">nextContext</span>
|
|
<span class="p">)</span>
|
|
|
|
<span class="kr">boolean</span> <span class="nx">shouldComponentUpdate</span><span class="p">(</span>
|
|
<span class="nx">object</span> <span class="nx">nextProps</span><span class="p">,</span> <span class="nx">object</span> <span class="nx">nextState</span><span class="p">,</span> <span class="nx">object</span> <span class="nx">nextContext</span>
|
|
<span class="p">)</span>
|
|
|
|
<span class="k">void</span> <span class="nx">componentWillUpdate</span><span class="p">(</span>
|
|
<span class="nx">object</span> <span class="nx">nextProps</span><span class="p">,</span> <span class="nx">object</span> <span class="nx">nextState</span><span class="p">,</span> <span class="nx">object</span> <span class="nx">nextContext</span>
|
|
<span class="p">)</span>
|
|
|
|
<span class="k">void</span> <span class="nx">componentDidUpdate</span><span class="p">(</span>
|
|
<span class="nx">object</span> <span class="nx">prevProps</span><span class="p">,</span> <span class="nx">object</span> <span class="nx">prevState</span><span class="p">,</span> <span class="nx">object</span> <span class="nx">prevContext</span>
|
|
<span class="p">)</span>
|
|
</code></pre></div><h2><a class="anchor" name="在无状态函数组件里引用-context"></a>在无状态函数组件里引用 context <a class="hash-link" href="#在无状态函数组件里引用-context">#</a></h2>
|
|
<p>如果 <code>contextTypes</code> 被定义为函数的属性，无状态函数同样能够引用<code>context</code>。下面的代码展示了被写为无状态函数组件的<code>Button</code>组件：</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">function</span> <span class="nx">Button</span><span class="p">(</span><span class="nx">props</span><span class="p">,</span> <span class="nx">context</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">(</span>
|
|
<span class="o"><</span><span class="nx">button</span> <span class="nx">style</span><span class="o">=</span><span class="p">{{</span><span class="nx">background</span><span class="o">:</span> <span class="nx">context</span><span class="p">.</span><span class="nx">color</span><span class="p">}}</span><span class="o">></span>
|
|
<span class="p">{</span><span class="nx">props</span><span class="p">.</span><span class="nx">children</span><span class="p">}</span>
|
|
<span class="o"><</span><span class="err">/button></span>
|
|
<span class="p">);</span>
|
|
<span class="p">}</span>
|
|
<span class="nx">Button</span><span class="p">.</span><span class="nx">contextTypes</span> <span class="o">=</span> <span class="p">{</span><span class="nx">color</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">string</span><span class="p">};</span>
|
|
</code></pre></div><h2><a class="anchor" name="更新context"></a>更新context <a class="hash-link" href="#更新context">#</a></h2>
|
|
<p>当state或props改变时，会调用<code>getChildContext</code>方法。为了能更新context内的数据，需要使用<code>this.setState</code>来触发组件state更新。这将会触发一个新的context，并且子组件也能接收变化。</p>
|
|
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">MediaQuery</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
|
|
<span class="nx">getInitialState</span><span class="o">:</span> <span class="kd">function</span><span class="p">(){</span>
|
|
<span class="k">return</span> <span class="p">{</span><span class="nx">type</span><span class="o">:</span><span class="s1">'desktop'</span><span class="p">};</span>
|
|
<span class="p">},</span>
|
|
<span class="nx">childContextTypes</span><span class="o">:</span> <span class="p">{</span>
|
|
<span class="nx">type</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">string</span>
|
|
<span class="p">},</span>
|
|
<span class="nx">getChildContext</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">{</span><span class="nx">type</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">state</span><span class="p">.</span><span class="nx">type</span><span class="p">};</span>
|
|
<span class="p">},</span>
|
|
<span class="nx">componentDidMount</span><span class="o">:</span> <span class="kd">function</span><span class="p">(){</span>
|
|
<span class="kd">var</span> <span class="nx">checkMediaQuery</span> <span class="o">=</span> <span class="kd">function</span><span class="p">(){</span>
|
|
<span class="kd">var</span> <span class="nx">type</span> <span class="o">=</span> <span class="nb">window</span><span class="p">.</span><span class="nx">matchMedia</span><span class="p">(</span><span class="s2">"(min-width: 1025px)"</span><span class="p">).</span><span class="nx">matches</span> <span class="o">?</span> <span class="s1">'desktop'</span> <span class="o">:</span> <span class="s1">'mobile'</span><span class="p">;</span>
|
|
<span class="k">if</span> <span class="p">(</span><span class="nx">type</span> <span class="o">!==</span> <span class="k">this</span><span class="p">.</span><span class="nx">state</span><span class="p">.</span><span class="nx">type</span><span class="p">){</span>
|
|
<span class="k">this</span><span class="p">.</span><span class="nx">setState</span><span class="p">({</span><span class="nx">type</span><span class="o">:</span><span class="nx">type</span><span class="p">});</span>
|
|
<span class="p">}</span>
|
|
<span class="p">};</span>
|
|
|
|
<span class="nb">window</span><span class="p">.</span><span class="nx">addEventListener</span><span class="p">(</span><span class="s1">'resize'</span><span class="p">,</span> <span class="nx">checkMediaQuery</span><span class="p">);</span>
|
|
<span class="nx">checkMediaQuery</span><span class="p">();</span>
|
|
<span class="p">},</span>
|
|
<span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">(){</span>
|
|
<span class="k">return</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">children</span><span class="p">;</span>
|
|
<span class="p">}</span>
|
|
<span class="p">});</span>
|
|
</code></pre></div><h2><a class="anchor" name="什么时候不用-context"></a>什么时候不用 context <a class="hash-link" href="#什么时候不用-context">#</a></h2>
|
|
<p>正如在写清晰代码时最好要避免使用全局变量一样，在大多数情况下，你应该避免使用context。特别是，在用它来"节省输入"和代替显式传入props时要三思。</p>
|
|
|
|
<p>隐式传入登录的用户，当前的语言，或者主题信息，是context最好的使用场景。要不然所有这些可能就是全局变量，但是context让你限定他们到一个单独的React树里。</p>
|
|
|
|
<p>在组件里传递你的模型数据时，不要依赖context。在组件树内显式传递数据，会更容易令人理解。之所以使用context会增加组件耦合度以及降低复用性，是因为组件在不同的地方渲染时，他们会表现出不同的行为。</p>
|
|
<h2><a class="anchor" name="已知的限制"></a>已知的限制 <a class="hash-link" href="#已知的限制">#</a></h2>
|
|
<p>假设由父组件提供的context值发生变动，但中间父级组件的<code>shouldComponentUpdate</code>返回了<code>false</code>，那么后代子级不会更新context。详见 issue <a href="https://github.com/facebook/react/issues/2517">#2517</a> 。</p>
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