import React, { Component } from 'react';

import './App.css';

import Child from './child'

class App extends Component {
  constructor(props){
    super(props);
    this.state={
      msg:'父類的消息',
      name:'John',
      age:99
    }
  }

  callback=(msg,name,age)=>{
    // setState方法,修改msg的值,值是由child里面?zhèn)鬟^來的
    this.setState({msg});
    this.setState({name});
    this.setState({age});
  }

 render() {
  return (
   <div className="App">
    <p> Message: &nbsp;&nbsp;{this.state.msg}</p>
    <Child callback={this.callback} age={this.state.age} name={this.state.name}></Child>
   </div>
  );
 }
}

export default App;

name={this.state.name} age={this.state.age}

<Child name={this.state.name} age={this.state.age}></Child>

import React from "react";

class Child extends React.Component{
  constructor(props){
    super(props);
    this.state={
      name:'Andy',
      age:31,
      msg:"來自子類的消息"
    }
  }

  change=()=>{
    this.props.callback(this.state.msg,this.state.name,this.state.age);
  }

  render(){
    return(
      <div>
        <div>{this.props.name}</div>
        <div>{this.props.age}</div>
        <button onClick={this.change}>點擊</button>
      </div>
    )
  }
}

export default Child;

change(){
}

this.change=this.change.bind(this)

onClick={this.change=this.change.bind(this)}