父组件需要向子组件传递一个函数，然后，子组件通过props获取函数并附上参数，最后，父组件通过函数拿到子组件传递的值。

父组件

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import React, { useState } from 'react';
import Child from './component/child';
import './index.less';
 
const Home: React.FC = () => {
  const [parentCount, setParentCountt] = useState<number>(0);
 
  const getChildCount = (val: number) => {
    setParentCountt(val);
  };
 
  return (
    <div className="home-wrap">
      <p>我是父组件</p>
      <p>子组件传过来的数字：{parentCount}</p>
      <Child getCount={getChildCount} />
    </div>
  );
};
 
export default Home;

子组件

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import React, { useState } from 'react';
 
type selfProps = {
  getCount: Function;
};
 
const Child: React.FC<selfProps> = (props) => {
  const { getCount } = props;
  const [count, setCount] = useState<number>(0);
 
  const addCount = (val: number) => {
    setCount(val);
    getCount(val);
  };
 
  return (
    <div className="child-wrap">
      <p>子组件</p>
      <p>数字：{count}</p>
      <button onClick={() => addCount(count + 1)}>数字递增</button>
    </div>
  );
};
 
export default Child;