taro 微信小程序 useImperativeHandle 问题

[必得设计]

组件代码 components/Demo/index.jsx

import Taro,{useImperativeHandle} from '@tarojs/taro';
import {View} from '@tarojs/components';

const Demo = ({childRef}) => {
  useImperativeHandle(childRef, () => ({
    stop () {
      console.log("======")
    }
  }))
  return (
      <View className="demo">111</View>
  )
}

export default Demo;

页面代码 pages/user.jsx

import Taro,{useRef} from '@tarojs/taro';
import {View, Button} from '@tarojs/components';
import Demo from '../components/Demo';

const User = () => {
  let childRef = useRef();

  const handelClick = () => {
    console.log(childRef.current);
    childRef.current.stop()
  }

  return(
      <View className="wrap wrap-user">
        <Button onClick={handelClick}>测试</Button>
        <Demo childRef={childRef} />
      </View>
  )
}

export default User;

这样无法在页面上执行到组件中到方法，点击报错。

请问这个是我的写法问题还是taro的问题， 使用hooks方式如何在父组件中调用子组件的方法。

taro info 信息如下

➜  MiniApp taro info 
👽 Taro v2.1.5


  Taro CLI 2.1.5 environment info:
    System:
      OS: macOS 10.15.4
      Shell: 5.7.1 - /bin/zsh
    Binaries:
      Node: 13.12.0 - ~/.nvm/versions/node/v13.12.0/bin/node
      Yarn: 1.22.4 - ~/.nvm/versions/node/v13.12.0/bin/yarn
      npm: 6.14.4 - ~/.nvm/versions/node/v13.12.0/bin/npm
    npmPackages:
      @tarojs/components: 2.1.5 => 2.1.5 
      @tarojs/components-qa: 2.1.5 => 2.1.5 
      @tarojs/mini-runner: 2.1.5 => 2.1.5 
      @tarojs/mobx: 2.1.5 => 2.1.5 
      @tarojs/mobx-h5: 2.1.5 => 2.1.5 
      @tarojs/router: 2.1.5 => 2.1.5 
      @tarojs/taro: 2.1.5 => 2.1.5 
      @tarojs/taro-alipay: 2.1.5 => 2.1.5 
      @tarojs/taro-h5: 2.1.5 => 2.1.5 
      @tarojs/taro-qq: 2.1.5 => 2.1.5 
      @tarojs/taro-quickapp: 2.1.5 => 2.1.5 
      @tarojs/taro-swan: 2.1.5 => 2.1.5 
      @tarojs/taro-tt: 2.1.5 => 2.1.5 
      @tarojs/taro-weapp: 2.1.5 => 2.1.5 
      @tarojs/webpack-runner: 2.1.5 => 2.1.5 
      eslint-config-taro: 2.1.5 => 2.1.5 
      eslint-plugin-taro: 2.1.5 => 2.1.5 
      nerv-devtools: ^1.5.6 => 1.5.6 
      nervjs: ^1.5.6 => 1.5.6 
      stylelint-config-taro-rn: 2.1.5 => 2.1.5 
      stylelint-taro-rn: 2.1.5 => 2.1.5 

[jd_66c33451e6eae]

需要引入 forwardRef