反應事件句柄OnChange

Question

我正在嘗試通過在app.js中執行onchange事件來更新標題組件的標題，但似乎無法正確綁定它們。 因此，當用戶輸入內容時，它將在標題組件中顯示文本。

APP.JS

 import React, { Component } from 'react';

    import './App.css';
    import Header from './Header';

    class App extends Component {

      constructor(props) {
        super(props);
       this.state = {name: "Michael"}

      }

       handleChange(e) {
         const name = e.target.value;
         this.changeTitle(name);
       }

      render() {
        return (
          <div className="App">
            <Header changeTitle={this.changeTitle.bind(this)} title={this.state.name}/>
            <p className="App-intro">
              Type here to change name.
            <input type="text" onChange={this.handleChange.bind(this)}/>
            </p>
          </div>
        );
      }
    }

    export default App;

HEADER.JS

import React, { Component } from 'react';
import logo from './logo.svg';

class Header extends Component {
  changeTitle(name) {
     this.setState({name});
   }
    render() {
        return (
            <div>
                <div className="App-header">
                    <img src={logo} className="App-logo" alt="logo" />
                    <h2>Welcome to React {this.props.name}</h2>
                </div>
            </div>
        );
    }
}

export default Header;

Answer 1

changeTitle函數應在App組件中定義，而不應在Header組件中定義。 實際上，您可以直接調用changeTitle組件，而不是從handleChange調用它，並且在Header組件中，以this.props.title而不是this.props.name身份訪問prop。

import React, { Component } from 'react';

import './App.css';
import Header from './Header';

class App extends Component {

  constructor(props) {
    super(props);
   this.state = {name: "Michael"}

  }
   changeTitle = (e) =>{
      this.setState({name: e.target.value});
    }

  render() {
    return (
      <div className="App">
        <Header title={this.state.name}/>
        <p className="App-intro">
          Type here to change name.
        <input type="text" onChange={this.changeTitle}/>
        </p>
      </div>
    );
  }
}

export default App;

並將其用作標題

import React, { Component } from 'react';
import logo from './logo.svg';

class Header extends Component {

    render() {
        return (
            <div>
                <div className="App-header">
                    <img src={logo} className="App-logo" alt="logo" />
                    <h2>Welcome to React {this.props.title}</h2>
                </div>
            </div>
        );
    }
}

export default Header;

工作片段：

  class App extends React.Component { constructor(props) { super(props); this.state = {name: "Michael"} } changeTitle = (e) =>{ this.setState({name: e.target.value}); } render() { return ( <div className="App"> <Header title={this.state.name}/> <p className="App-intro"> Type here to change name. <input type="text" onChange={this.changeTitle}/> </p> </div> ); } } class Header extends React.Component { render() { var logo = 'https://processing.org/tutorials/pixels/imgs/tint1.jpg'; return ( <div> <div className="App-header"> <img src={logo} className="App-logo" alt="logo" /> <h2>Welcome to React {this.props.title}</h2> </div> </div> ); } } ReactDOM.render(<App/>, document.getElementById('app')) 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script> <div id="app"></div> 

Answer 2

您無需將change事件傳遞給Header組件，只需傳遞數據並在App組件中執行setState 。

原因是您僅使用Header組件顯示標題名稱，因此狀態應由父組件App管理。

檢查工作片段：

 class App extends React.Component { constructor(props) { super(props); this.state = {name: "Michael"} } handleChange(e) { const name = e.target.value; this.setState({name}); //do the setState here } render() { return ( <div className="App"> <Header title={this.state.name}/> <p className="App-intro"> Type here to change name. <input type="text" onChange={this.handleChange.bind(this)}/> </p> </div> ); } } class Header extends React.Component { render() { return ( <div> <div className="App-header"> <img src={''} className="App-logo" alt="logo" /> <h2>Welcome to React {this.props.title}</h2> </div> </div> ); } } ReactDOM.render(<App/>, document.getElementById('app')) 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script> <div id='app'/>