父组件通过props把方法传递给子组件

class Parent extends React.Component {
    getRef(ref){
        this.node = ref
    }
    render(){
        return(
            <Children getRef = {this.getRef} />
        )
    }
}

子组件一旦创建就会执行ref的回调

function Children (props) {
    return(
        <>
            <input ref={props.getRef} />
        </>
    )
    
}