react 父子组件通信

1.父组件向子组件传值

父组件

import React from "react"
import ChildrenList from "./ChildrenList "

class Comment extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
          arr: [{
                "userName": "fangMing", "text": "方明", "result": true
            },{
                "userName": "liSi", "text": "黎明", "result": true
            },]
         }
   }

render() {
      return (
        <div>
           <ChildrenList arr={this.state.arr} />  //这里把state里面的arr传递到子组件
        </div>
      )
}



}


export default Comment;

子组件

import React from "react"

class ChildrenList extends React.Component {
    constructor(props) {
        super(props);
   }

render() {
      return (
      <div className="list">
                <ul>
                    {
                        this.props.arr.map(item => { //这个地方通过this.props.arr接收到父组件传过来的arr，然后在{}里面进行js的循环
                            return (
                                <li key={item.userName}>
                                    {item.userName} 评论是:{item.text}
                                </li>
                            )
                        })
                    }
                </ul>
             
            </div>
      )
}



}


export default ChildrenList ;

2.子组件向父组件传值

父组件

import React from "react"
import ChildrenList from "./ChildrenList "
 
class Comment extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            parentText: "this is parent text",   
             arr: [{
                "userName": "fangMing", "text": "方明", "result": true
            },{
                "userName": "liSi", "text": "黎明", "result": true
            },]
        }
    }
 
    fn(data) {
        this.setState({
            parentText: data //把父组件中的parentText替换为子组件传递的值
        },() =>{
           console.log(this.state.parentText);//setState是异步操作，但是我们可以在它的回调函数里面进行操作
        });
 
    }
 
 
 
    render() {
        return (
            <div>
                //通过绑定事件进行值的运算，这个地方一定要记得.bind(this)，
            不然会报错，切记切记，因为通过事件传递的时候this的指向已经改变
                <ChildrenList arr={this.state.arr} pfn={this.fn.bind(this)} />
                <p>
                    text is {this.state.parentText}
                </p>
        
            </div>
 
        )
    }
}
 
export default Comment; 

子组件

import React from "react"
 
class ChildrenList extends React.Component {
    constructor(props) {
        super(props);
        this.state = ({
            childText: "this is child text"
        })
 
    }
    clickFun(text) {
        this.props.pfn(text)//这个地方把值传递给了props的事件当中
    }
    render() {
        return (
            <div className="list">
                <ul>
                    {
                        this.props.arr.map(item => {
                            return (
                                <li key={item.userName}>
                                    {item.userName} 评论是:{item.text}
                                </li>
                            )
                        })
                    }
                </ul>
                //通过事件进行传值，如果想得到event，可以在参数最后加一个event，
                这个地方还是要强调，this，this，this
                <button onClick={this.clickFun.bind(this, this.state.childText)}>
                    click me
                </button>
            </div>
        )
    }
}
 
export default ChildrenList ;