子组件：

import {useState, useImperativeHandle,forwardRef} from 'react'
//props子组件需要接收 ref

const ChildComp = (props, ref) => {

    const [val, setVal] = useState('')
    // 此处注意useImperativeHandle方法的的第一个参数是目标元素的ref引用
    useImperativeHandle(ref, () => ({
        // changeVal 就是暴露给父组件的方法, newVal是父组件传递的参数
        changeVal: (newVal) => {
          setVal(newVal)
        }
    }))
  return (
    <div>{val}</div>
 )
}
ChildComp = forwardRef(ChildComp)

export default ChildComp

父组件：

import {useRef} from 'react'
import ChildComp from './ChildComp.jsx'

const FComp = () => {
    const childRef = useRef(null)
    const updateChildState = () => {
        // changeVal就是子组件暴露给父组件的方法
        childRef.current.changeVal(99);
    }
    
    return (
      <>
        <ChildComp ref={childRef}></ChildComp>
        <button onClick={updateChildState}>触发子组件方法</button>
      </>
    )
}
export default FComp