React父组件调用子组件的方法--ref方法

import React, { Component } from 'react'

class ChildNode extends Component {
  constructor(props){
    super(props)
    this.state={
      count:1
    }
  }
  addCount=()=>{
    let newCount = this.state.count+1;
    this.setState({
      count:newCount
    })
  }
  render() {
    return (
      <div>
        <p>子组件</p>
        <p>{this.state.count}</p>
        <button onClick={this.addCount}>点我+1</button>
      </div>
    )
  }
}
class ParentNode extends Component {
  state={
    num:1
  }
  childRef = React.createRef();
  logRef=()=>{
    // console.log(this.childRef.current)
    // this.childRef.current.addCount()

    // 使用函数式绑定ref就得使用下面这种获取方法
    console.log(this.childRef)
    this.childRef.addCount()
  }
  render() {
    return (
      <div>
        <h3>父组件</h3>
        <button onClick={this.logRef}>打印且调用子组件的方法</button>
        {/* 简单的使用ref获取dom */}
        {/* <ChildNode ref={this.childRef}/> */}
        {/* 使用函数式绑定ref*/}
        <ChildNode ref={el=>this.childRef=el}/>
      </div>
    )
  }
}
export default ParentNode