63 lines
1.5 KiB
Markdown
63 lines
1.5 KiB
Markdown
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---
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title: Optimize Re-Renders with shouldComponentUpdate
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localeTitle: 使用shouldComponentUpdate优化重新渲染
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---
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## 使用shouldComponentUpdate优化重新渲染
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## 暗示：
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检查`nextProps`的值是否均匀。
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## 解：
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对于此解决方案，您将使用`if/then`语句来检查`nextProps`的值是否为偶数。 `nextProps`与`props`不同之处在于它是一个尚未在UI中呈现的值，因此在`shouldComponentUpdate()`方法中，您基本上要求使用`nextProps`值更新UI的`nextProps` 。
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```jsx
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class OnlyEvens extends React.Component {
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constructor(props) {
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super(props);
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}
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shouldComponentUpdate(nextProps, nextState) {
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console.log('Should I update?');
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// change code below this line
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if (nextProps.value % 2 == 0) {
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return true;
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}
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return false;
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// change code above this line
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}
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componentWillReceiveProps(nextProps) {
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console.log('Receiving new props...');
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}
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componentDidUpdate() {
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console.log('Component re-rendered.');
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}
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render() {
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return <h1>{this.props.value}</h1>
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}
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};
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class Controller 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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value: 0
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};
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this.addValue = this.addValue.bind(this);
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}
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addValue() {
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this.setState({
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value: this.state.value + 1
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});
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}
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render() {
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return (
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<div>
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<button onClick={this.addValue}>Add</button>
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<OnlyEvens value={this.state.value}/>
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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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