React - useRef with TypeScript and functional component

Question

I was trying to call the child component method from parent component and I was trying to use useRef. In the future, the SayHi method will be update hook state in the child component. Unfortunately, I have bugs with I can't deal with.

Line: ref.current.SayHi();

Property 'SayHi' does not exist on type 'ForwardRefExoticComponent<{ name: string; } & RefAttributes<{ SayHi: () => void; }>>'.

Line: < Child name="Adam" ref={ref}/>

Type 'RefObject void; }>>>' is not assignable to type '((instance: { SayHi: () => void; } | null) => void) | RefObject<{ SayHi: () => void; }> | null | undefined'. Type 'RefObject void; }>>>' is not assignable to type 'RefObject<{ SayHi: () => void; }>'. Property 'SayHi' is missing in type 'ForwardRefExoticComponent<{ name: string; } & RefAttributes<{ SayHi: () => void; }>>' but required in type '{ SayHi: () => void; }'.

Full test.tsx file:

import React, { useRef, forwardRef, useImperativeHandle, Ref } from 'react'

const Parent = () => {
    const ref = useRef<typeof Child>(null);
    const onButtonClick = () => {
      if (ref.current) {
        ref.current.SayHi();
      }
    };
    return (
      <div>
        <Child name="Adam" ref={ref}/>
        <button onClick={onButtonClick}>Log console</button>
      </div>
    );
  }

const Child = forwardRef((props: {name: string}, ref: Ref<{SayHi: () => void}>)=> {
  const {name} = props;
  useImperativeHandle(ref, () => ({ SayHi }));

  function SayHi() { console.log("Hello " + name); }

  return <div>{name}</div>;
});

I deeply ask for help on this topic.

Answer 1

You require to extract the ref type elsewhere:

interface RefObject {
  SayHi: () => void
}

then just refer to it in both places

const Child = forwardRef((props: {name: string}, ref: Ref<RefObject>)=> {
  const {name} = props;  
  useImperativeHandle(ref, () => ({ SayHi }));
  function SayHi() { console.log("Hello " + name); }

  return <div>{name}</div>;
});

const Parent = () => {
    const ref = useRef<RefObject>(null);
    const onButtonClick = () => {
      if (ref.current) {
        ref.current.SayHi();
      }
    };
    return (
      <div>
        <Child name="Adam" ref={ref}/>
        <button onClick={onButtonClick}>Log console</button>
      </div>
    );
}

Answer 2

只需用这个const ref = useRef<{ SayHi: () => void }>(null);替换你的ref的声明const ref = useRef<{ SayHi: () => void }>(null);