96 lines
5.1 KiB
Markdown
96 lines
5.1 KiB
Markdown
---
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id: 5a24c314108439a4d4036189
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title: Change Inline CSS Conditionally Based on Component State
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challengeType: 6
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isRequired: false
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videoUrl: ''
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localeTitle: 有条件地改变内联CSS基于组件状态
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---
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## Description
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<section id="description">此时，您已经看到了条件渲染的几个应用程序以及内联样式的使用。这是另外一个结合了这两个主题的例子。您还可以根据React组件的状态有条件地呈现CSS。要执行此操作，请检查条件，如果满足该条件，则修改在render方法中分配给JSX元素的样式对象。这个范例很重要，因为它是通过直接修改DOM元素来应用样式的更传统方法的一种戏剧性转变（例如，jQuery非常常见）。在该方法中，您必须跟踪元素何时更改并直接处理实际操作。跟踪更改可能变得很困难，可能会使您的UI无法预测。根据条件设置样式对象时，您将描述UI应如何看作应用程序状态的函数。有明确的信息流只能向一个方向移动。使用React编写应用程序时，这是首选方法。 </section>
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## Instructions
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<section id="instructions">代码编辑器有一个简单的受控输入组件，带有样式边框。如果用户在输入框中键入超过15个字符的文本，则希望将此边框设置为红色。添加条件以检查此情况，如果条件有效，则将输入边框样式设置为<code>3px solid red</code> 。您可以通过在输入中输入文本来尝试。 </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>GateKeeper</code>组件应该呈现<code>div</code>元素。
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testString: 'assert((function() { const mockedComponent = Enzyme.mount(React.createElement(GateKeeper)); return mockedComponent.find("div").length === 1; })(), "The <code>GateKeeper</code> component should render a <code>div</code> element.");'
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- text: 应使用设置为空字符串的状态键<code>input</code>初始化<code>GateKeeper</code>组件。
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testString: 'assert((function() { const mockedComponent = Enzyme.mount(React.createElement(GateKeeper)); return mockedComponent.state().input === ""; })(), "The <code>GateKeeper</code> component should be initialized with a state key <code>input</code> set to an empty string.");'
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- text: <code>GateKeeper</code>组件应呈现<code>h3</code>标记和<code>input</code>标记。
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testString: 'assert((function() { const mockedComponent = Enzyme.mount(React.createElement(GateKeeper)); return mockedComponent.find("h3").length === 1 && mockedComponent.find("input").length === 1; })(), "The <code>GateKeeper</code> component should render an <code>h3</code> tag and an <code>input</code> tag.");'
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- text: <code>input</code>标记最初应为<code>border</code>属性的<code>1px solid black</code>样式。
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testString: 'assert((function() { const mockedComponent = Enzyme.mount(React.createElement(GateKeeper)); return mockedComponent.find("input").props().style.border === "1px solid black"; })(), "The <code>input</code> tag should initially have a style of <code>1px solid black</code> for the <code>border</code> property.");'
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- text: 如果状态中的输入值超过15个字符，则<code>input</code>标记应使用<code>3px solid red</code>边框进行样式设置。
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testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100)); const mockedComponent = Enzyme.mount(React.createElement(GateKeeper)); const simulateChange = (el, value) => el.simulate("change", {target: {value}}); let initialStyle = mockedComponent.find("input").props().style.border; const state_1 = () => { mockedComponent.setState({input: "this is 15 char" }); return waitForIt(() => mockedComponent.find("input").props().style.border )}; const state_2 = () => { mockedComponent.setState({input: "A very long string longer than 15 characters." }); return waitForIt(() => mockedComponent.find("input").props().style.border )}; const style_1 = await state_1(); const style_2 = await state_2(); assert(initialStyle === "1px solid black" && style_1 === "1px solid black" && style_2 === "3px solid red", "The <code>input</code> tag should be styled with a border of <code>3px solid red</code> if the input value in state is longer than 15 characters."); }; '
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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 GateKeeper 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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input: "
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};
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this.handleChange = this.handleChange.bind(this);
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}
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handleChange(event) {
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this.setState({ input: event.target.value })
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}
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render() {
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let inputStyle = {
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border: '1px solid black'
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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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return (
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<div>
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<h3>Don't Type Too Much:</h3>
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<input
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type="text"
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style={inputStyle}
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value={this.state.input}
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onChange={this.handleChange} />
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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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</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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