ForwardRef useImperativeHandle方法demo

export class RefTest extends React.Component {
    currentDom: React.RefObject<HTMLDivElement> = React.createRef();
    currentChildren: React.LegacyRef<Children> = React.createRef();
    render() {
        console.log(this.currentChildren, this.currentDom);
    return (
        <>
            <div ref = { this.currentDom }>你好</div>
            <Children ref = { this.currentChildren}></Children>
        </>
       )
    }
}

export const RefTest = () => {
    const currentDom = useRef(null);
    const currentChildren = useRef(null);
    useEffect(() => {
        console.log(currentChildren, currentDom, '这里也可以打印出来了');
     },[])
   return (
   <>
       <div ref = { currentDom }>你好</div>
       <Children ref = { currentChildren }></Children>
   </>
    )
}

import React, { useEffect } from 'react';
class Son extends React.Component{
    state={
        sonValue:''
    }
    render(){
    return <div>
        <div>子组件的信息： {this.state.sonValue}</div>
        <div>对父组件说</div>
        <input onChange{(e)=>this.props.setFather(e.target.value)}/>
        </div>
    }
}
export default function Father(){
const [ fatherValue , setFatherValue ] = React.useState('')
const sonRef = React.useRef(null)
return <div>
    <div>父组件的信息： {fatherValue}</div>
    <div>对子组件说</div>
    <input onChange = { (e) => sonRef.current.setState( {sonValue: e.target.value})}/>
    <Son ref={sonRef} setFather={setFatherValue}/>
    </div>
}

![图片转存失败，建议将图片保存下来直接上传
        import React from 'react';
interface IProps {
    targetRef: React.RefObject<HTMLDivElement>
    otherProps: string
}
interface IGrandParentProps {
    otherProps: string
}
class Son extends React.Component<IProps> {
    constructor(props) {
        super(props);
        console.log(props,'son中的props');
     }
     render() {
         // 最终目标是获取该DOM元素的信息
         return <div ref= { this.props.targetRef }>真正目的是这个</div>
     }
}
class Farther extends React.Component<IProps> {
    constructor(props) {
        super(props)
        console.log(props, 'father中的props');
    }
    render() {
        return (
        // 继续将ref传给Son
            <Son targetRef={this.props.targetRef} {...this.props} />
         )
    }
}
// 在这里使用了forwardRef， 相当于把传入的ref转发给Father组件
const ForwardRef = React.forwardRef((props: IGrandParentProps, ref: React.RefObject<HTMLDivElement>) 
    => <Farther targetRef={ref} {...props}/>)

 image.png(https://p3-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/5d49e7ff4ec940b28dcb3a780fd5c0a7~tplv-k3u1fbpfcp-watermark.image?)
export class GrandFather extends React.Component {
    currentRef:React.RefObject<HTMLDivElement> = React.createRef();
    componentDidMount() {
        // 获取到的Ref信息
        console.log(this.currentRef, 'componentDidMount');
    }
    render() {
        return (
        <ForwardRef ref={this.currentRef} otherProps = '正常传递其他props' />
        )
    }
}
]()

import { forwardRef, useEffect, useImperativeHandle, useRef, useState } from "react"
const ForwardItem = forwardRef((props, ref) => {
    const [sonValue, setSonValue] = useState('修改之前的值');
    useImperativeHandle(ref, () => ({
        setSonValue,
    }))
    return (
        <div>子组件的值： {sonValue}</div>
    )
})
export const Father = () => {
    const testRef = useRef(null);
    useEffect(() => {
        console.log(testRef.current, 'ref获取到的信息')
     })
    const changeValue = () => {
        const DURATION = 2000;
        setTimeout(() => {
        testRef.current.setSonValue('我已经修改值啦')
        },DURATION)
    }
    return (
    <>
       <ForwardItem ref={ testRef }/>
       <button onClick={() => changeValue()}>2s后修改子组件ForwardItem的值</button>
    </>
    )
}

const ForwardItem = forwardRef((props, ref) => {
    const elementRef: RefObject<HTMLDivElement> = useRef();
    useImperativeHandle(ref, () => ({
        elementRef,
    }))
    return (
        <div ref = { elementRef }>我是一个子组件</div>
     )
})
export const Father = () => {
    const testRef = useRef(null);
    useEffect(() => {
        console.log(testRef.current, 'ref获取到的信息')
     })
    return (
    <>
        <ForwardItem ref={ testRef }/>
    </>
    )
}