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Dan Abramov
557 lines
22 KiB
HTML
557 lines
22 KiB
HTML
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<title>组件 API | React</title>
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<h3>Tips</h3>
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<a href="/react/tips/introduction.html">Introduction</a>
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<a href="/react/tips/maximum-number-of-jsx-root-nodes.html">Maximum Number of JSX Root Nodes</a>
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<li>
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<a href="/react/tips/style-props-value-px.html">Shorthand for Specifying Pixel Values in style props</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/controlled-input-null-value.html">Value of null for Controlled Input</a>
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<a href="/react/tips/componentWillReceiveProps-not-triggered-after-mounting.html">componentWillReceiveProps Not Triggered After Mounting</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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<li>
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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/initial-ajax.html">Load Initial Data via AJAX</a>
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<li>
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<a href="/react/tips/false-in-jsx.html">False in JSX</a>
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<li>
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<a href="/react/tips/communicate-between-components.html">Communicate Between Components</a>
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<li>
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<a href="/react/tips/expose-component-functions.html">Expose Component Functions</a>
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<li>
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<a href="/react/tips/children-undefined.html">this.props.children undefined</a>
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<li>
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<a href="/react/tips/use-react-with-other-libraries.html">Use React with Other Libraries</a>
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</li>
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<li>
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<a href="/react/tips/dangerously-set-inner-html.html">Dangerously Set innerHTML</a>
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</li>
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<!-- Contributing Nav -->
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<h3>Contributing</h3>
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<ul>
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<li>
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<a href="/react/contributing/how-to-contribute.html">How to Contribute</a>
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</li>
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<li>
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<a href="/react/contributing/codebase-overview.html">Codebase Overview</a>
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</li>
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<li>
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<a href="/react/contributing/design-principles.html">Design Principles</a>
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</li>
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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/ref-02-component-api.zh-CN.md" target="_blank">Edit on GitHub</a>
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<h1>
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组件 API
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</h1>
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<div class="subHeader"></div>
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<h2><a class="anchor" name="react.component"></a>React.Component <a class="hash-link" href="#react.component">#</a></h2>
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<p>当渲染时，React 组件的实例在 React 内部被创建。这些实例在随后的渲染中被重复使用，并可以在组件方法中通过 <code>this</code> 访问。唯一的在 React 之外获取 React 组件实例句柄的方法是保存 <code>ReactDOM.render</code> 的返回值。在其它组件内，你可以使用 <a href="/react/docs/more-about-refs-zh-CN.html">refs</a> 得到相同的结果。</p>
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<h3><a class="anchor" name="setstate"></a>setState <a class="hash-link" href="#setstate">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">setState</span><span class="p">(</span>
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<span class="kd">function</span><span class="o">|</span><span class="nx">object</span> <span class="nx">nextState</span><span class="p">,</span>
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<span class="p">[</span><span class="kd">function</span> <span class="nx">callback</span><span class="p">]</span>
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<span class="p">)</span>
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</code></pre></div>
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<p>执行一个 nextState 到当前 state 的浅合并。这是你从事件处理器和服务器请求回调用来触发 UI 更新的主要手段。</p>
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<p>第一个参数可以是一个对象（包含0或者多个keys来更新）或者一个（state 和 props的）函数，它返回一个包含要更新的keys的对象。</p>
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<p>这里是一个简单的运用:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">setState</span><span class="p">({</span><span class="nx">mykey</span><span class="o">:</span> <span class="s1">'my new value'</span><span class="p">});</span>
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</code></pre></div>
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<p>也可以以 <code>function(state, props)</code> 传递一个函数。当你想要把一个在设置任何值之前参考前一次 state+props 的值的原子更新放在队列中 这会有很用。例如，假如我们想在 state 增加一个值:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">setState</span><span class="p">(</span><span class="kd">function</span><span class="p">(</span><span class="nx">previousState</span><span class="p">,</span> <span class="nx">currentProps</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">return</span> <span class="p">{</span><span class="nx">myInteger</span><span class="o">:</span> <span class="nx">previousState</span><span class="p">.</span><span class="nx">myInteger</span> <span class="o">+</span> <span class="mi">1</span><span class="p">};</span>
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<span class="p">});</span>
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</code></pre></div>
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<p>第二个（可选）的参数是一个将会在 <code>setState</code> 完成和组件被重绘后执行的回调函数。</p>
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<blockquote>
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<p>注意:</p>
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<p><em>绝对不要</em> 直接改变 <code>this.state</code>，因为之后调用 <code>setState()</code> 可能会替换掉你做的改变。把 <code>this.state</code> 当做是不可变的。</p>
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<p><code>setState()</code> 不会立刻改变 <code>this.state</code>，而是创建一个即将处理的 state 转变。在调用该方法之后访问 <code>this.state</code> 可能会返回现有的值。</p>
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<p>对 <code>setState</code> 的调用没有任何同步性的保证，并且调用可能会为了性能收益批量执行。</p>
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<p><code>setState()</code> 将总是触发一次重绘，除非在 <code>shouldComponentUpdate()</code> 中实现了条件渲染逻辑。如果可变对象被使用了，但又不能在 <code>shouldComponentUpdate()</code> 中实现这种逻辑，仅在新 state 和之前的 state 存在差异的时候调用 <code>setState()</code> 可以避免不必要的重新渲染。</p>
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</blockquote>
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<h3><a class="anchor" name="replacestate"></a>replaceState <a class="hash-link" href="#replacestate">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">replaceState</span><span class="p">(</span>
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<span class="nx">object</span> <span class="nx">nextState</span><span class="p">,</span>
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|
<span class="p">[</span><span class="kd">function</span> <span class="nx">callback</span><span class="p">]</span>
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<span class="p">)</span>
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</code></pre></div>
|
|
<p>类似于 <code>setState()</code>，但是删除任何 先前存在但不在 nextState 里的 state 键。</p>
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|
|
|
<blockquote>
|
|
<p>注意:</p>
|
|
|
|
<p>这个方法在从 <code>React.Component</code> 扩展的 ES6 <code>class</code> 组件里不可用。它也许会在未来的 React 版本中被完全移除。</p>
|
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</blockquote>
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|
<h3><a class="anchor" name="forceupdate"></a>forceUpdate <a class="hash-link" href="#forceupdate">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">forceUpdate</span><span class="p">(</span>
|
|
<span class="p">[</span><span class="kd">function</span> <span class="nx">callback</span><span class="p">]</span>
|
|
<span class="p">)</span>
|
|
</code></pre></div>
|
|
<p>默认情况下，当你的组件的 state 或者 props 改变，你的组件将会重绘。然而，如果它们隐式的改变（例如：在对象深处的数据改变了但没有改变对象本身）或者如果你的 <code>render()</code> 方法依赖于其他的数据，你可以用调用 <code>forceUpdate()</code> 来告诉 React 它需要重新运行 <code>render()</code>。</p>
|
|
|
|
<p>调用 <code>forceUpdate()</code> 将会导致 <code>render()</code> 跳过 <code>shouldComponentUpdate()</code> 在组件上被调用，这会为子级触发正常的生命周期方法。包括每个子级的 <code>shouldComponentUpdate()</code> 方法。如果标记改变了，React 仍仅只更新 DOM。</p>
|
|
|
|
<p>通常你应该试着避免所有对 <code>forceUpdate()</code> 的使用并且在 <code>render()</code> 里只从 <code>this.props</code> 和 <code>this.state</code> 读取。这会使你的组件 "纯粹" 并且你的组件会更简单和高效。</p>
|
|
<h3><a class="anchor" name="ismounted"></a>isMounted <a class="hash-link" href="#ismounted">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kr">boolean</span> <span class="nx">isMounted</span><span class="p">()</span>
|
|
</code></pre></div>
|
|
<p>如果组件渲染到了 DOM 中，<code>isMounted()</code> 返回 true，否则返回 <code>false</code>。可以使用该方法来控制对 <code>setState()</code> 和 <code>forceUpdate()</code> 的异步调用。</p>
|
|
|
|
<blockquote>
|
|
<p>注意:</p>
|
|
|
|
<p>这个方法在从 <code>React.Component</code> 扩展的 ES6 <code>class</code> 组件里不可用。它也许会在未来的 React 版本中被完全移除,所以你也要移除它 <a href="/react/blog/2015/12/16/ismounted-antipattern.html">start migrating away from isMounted() now</a></p>
|
|
</blockquote>
|
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