92 lines
4.0 KiB
Markdown
92 lines
4.0 KiB
Markdown
---
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id: 5a24c314108439a4d4036176
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title: Use State to Toggle an Element
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challengeType: 6
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isRequired: false
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videoUrl: ''
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localeTitle: 使用State切换元素
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---
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## Description
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<section id="description">您可以以比您目前所见的更复杂的方式在React应用程序中使用<code>state</code> 。一个示例是监视值的状态，然后根据此值有条件地呈现UI。有几种不同的方法可以实现这一点，代码编辑器显示了一种方法。 </section>
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## Instructions
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<section id="instructions"> <code>MyComponent</code>有一个<code>visibility</code>属性，初始化为<code>false</code> 。如果<code>visibility</code>值为true，则render方法返回一个视图;如果为false，则返回不同的视图。目前，无法更新组件<code>state</code>的<code>visibility</code>属性。该值应在true和false之间来回切换。按钮上有一个单击处理程序，它触发一个名为<code>toggleVisibility()</code>的类方法。定义此方法，以便在调用方法时， <code>visibility</code> <code>state</code>切换为相反的值。如果<code>visibility</code>是<code>false</code> ，该方法将其设置为<code>true</code> ，反之亦然。最后，单击按钮以根据其<code>state</code>查看组件的条件呈现。 <strong>提示：</strong>不要忘记将<code>this</code>关键字绑定到构造函数中的方法！ </section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>MyComponent</code>应该返回一个包含<code>button</code>的<code>div</code>元素。
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testString: 'assert.strictEqual(Enzyme.mount(React.createElement(MyComponent)).find("div").find("button").length, 1, "<code>MyComponent</code> should return a <code>div</code> element which contains a <code>button</code>.");'
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- text: <code>MyComponent</code>的状态应该初始化，并将<code>visibility</code>属性设置为<code>false</code> 。
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testString: 'assert.strictEqual(Enzyme.mount(React.createElement(MyComponent)).state("visibility"), false, "The state of <code>MyComponent</code> should initialize with a <code>visibility</code> property set to <code>false</code>.");'
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- text: 单击按钮元素应该在<code>true</code>和<code>false</code>之间切换状态的<code>visibility</code>属性。
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testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250)); const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); const first = () => { mockedComponent.setState({ visibility: false }); return waitForIt(() => mockedComponent.state("visibility")); }; const second = () => { mockedComponent.find("button").simulate("click"); return waitForIt(() => mockedComponent.state("visibility")); }; const third = () => { mockedComponent.find("button").simulate("click"); return waitForIt(() => mockedComponent.state("visibility")); }; const firstValue = await first(); const secondValue = await second(); const thirdValue = await third(); assert(!firstValue && secondValue && !thirdValue, "Clicking the button element should toggle the <code>visibility</code> property in state between <code>true</code> and <code>false</code>."); }; '
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='jsx-seed'>
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```jsx
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class MyComponent extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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visibility: false
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};
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// change code below this line
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// change code above this line
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}
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// change code below this line
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// change code above this line
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render() {
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if (this.state.visibility) {
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return (
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<div>
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<button onClick={this.toggleVisibility}>Click Me</button>
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<h1>Now you see me!</h1>
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</div>
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);
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} else {
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return (
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<div>
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<button onClick={this.toggleVisibility}>Click Me</button>
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</div>
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);
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}
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}
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};
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```
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</div>
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### After Test
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<div id='jsx-teardown'>
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```js
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console.info('after the test');
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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```
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</section>
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