react组件传值

1. 父子传值

父传子使用props，父组件更新视图改变props子组件会同步更新。

类组件

import React, { Component } from 'react';

class Father extends Component { 

    state={
        count: 0
    }

    render(){
        return (
            <Child count={count} />
        )
    }
}

class Child extends Component {

    constructor(){
        super(props); // 必须先用super方法传入props，才能在constructor中使用this.props
        console.log(this.props); // 0
    }

    return (
        <div>{this.props.count}</div> // 0
    )
}

函数组件

import { useState, useEffect } from 'react';

function Father(){

    const [ count, setCount ] = useState(0);

    return (
        <Child count={count} />
    )
}
// 需要传入props参数
function Child(props){

    console.log(props.count); // 0

    useEffect(()=>{
        console.log(props.count); // 0
    },[])

    return (
        <div>{props.count}</div> // 0
    )
}

子传父使用回调函数以参数的形式返回给父组件

类组件

import React,{Component} from 'react';
import {Button} from 'antd'; 

class Father extends Component{
    result(params){
        console.log(params); // 'aaa'
    }
    render(){
        return (
            <div>
                <div>父组件</div>
                <Child back={(params)=>{this.result(params)}} />
            </div>
        )
    }

}

class Child extends Component{
    render(){
        return (
            <Button type="primary" onClick={()=>{this.props.back('aaa')}}>我是子组件，点击我将子组件数据传到父组件</Button>
        )
    }

}

函数组件

import {Button} from 'antd'; 

function Father(){
    const result = (params)=>{
        console.log(params); // 'aaa'
    }
    return (
        <div>
            <div>父组件</div>
            <Child back={(params)=>{ result(params) }}/>
        </div>
    )
}
// 记得传入props参数
function Child(props){
    return (
        <Button type="primary" onClick={()=>{props.back('aaa')}}>我是子组件，点击我将子组件数据传到父组件</Button>
    )
}

父组件调用子组件的方法

类组件

import React,{Component} from 'react';
import { Button } from 'antd';

class Father extends Component{
    handle(){
        this.Child.func()
    }
    render(){
        return (
            <div>
                <Button type="primary" onClick={()=>{this.handle()}}>我是父组件，点击我获取子组件方法</Button>
                <Child onRef={node=>{this.Child = node}} />
             </div>
        )
    }
}

class Child extends Component{
   componentDidMount(){
       this.props.onRef && this.props.onRef(this);
   }
    func(){
        console.log('我是子组件方法！')
    }
    render(){
        return (
            <div>我是子组件</div>
        )
    }
}

函数组件

import { useImperativeHandle } from 'react';
import { Button } from 'antd';

function Father() {
  const handle = () => {
    ChildRef.current.func();
  }
  let ChildRef = React.createRef();
  return (
    <div>
      <div>
        <Button type="primary" onClick={handle}>我是父组件，点击我调用子组件方法</Button>
      </div>
      <Child onRef={ChildRef} />
    </div>
  )
}
function Child(props) {
  // 用useImperativeHandle暴露外部ref能访问的属性和方法
  useImperativeHandle(props.onRef, () => {
    return {
      func: func
    }
  })
  const func = () => {
    console.log('我是子组件方法')
  }
  return (
    <div>子组件</div>
  )
}