React setState不重新呈现

Question

import React from 'react';

class Button extends React.Component {
  constructor(props){
      super(props)
      this.state = {
          id : props.id
      }
  }
  render() {
      console.log('Button state id is', this.state.id)
      return(
          <div>
              'hi ' +  {this.state.id}
              <br/>
              <button type='submit' onClick={this.props.handleSubmit}>
                  submit
              </button>
          </div>
      )
  }
}

export default class App extends React.Component {
  constructor(props) {
      super(props)
      this.state = {
          id: 1
      }
      this.changeId = this.changeId.bind(this)
  }
  changeId() {
      let id = this.state.id
      console.log('parent state id is', id)
      this.setState({
          id: ++id
      })
  }
  render() {
      return(
          <Button id={this.state.id} handleSubmit={this.changeId}/>
      )
  }
}

Answer 1

要在子组件中重新呈现数字，您需要对代码进行以下更改：

在当前场景中，changeId函数中的id值是event，所以不能做++id。您必须将其更新为：

changeId() {
    this.setState({
        id: ++this.state.id
    })
}

对于子组件重新呈现道具值，您必须监听道具是否有任何变化。为此，使用componentDidUpdate React的生命周期。像这样：

componentDidUpdate(prevProps){
   if (this.props.id !== prevProps.id) {
    this.setState({id: this.props.id});
  }
}

class Button extends React.Component {

  render() {
      return(
          <div>
              'hi ' +  {this.props.id}
              <br/>
              <button type='submit' onClick={this.props.handleSubmit}>
                  submit
              </button>
          </div>
      )
    }
}

class App extends React.Component {
  constructor(props) {
      super(props)
      this.state = {
          id: 1
      }
      this.changeId = this.changeId.bind(this)
  }
  changeId() {
      this.setState({
          id: ++this.state.id
      })
  }
  render() {
      return(
          <Button id={this.state.id} handleSubmit={this.changeId}/>
      )
    }
}

ReactDOM.render(<App />, document.getElementById('root'))

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
<div id="root" />