如何在功能组件中从父组件更改子组件 state

Question

我创建了一个倒数计时器组件，并且在该组件附近有一个按钮

我想当用户点击这个按钮时，重置计时器

为此我应该改变孩子 state

我找到了从孩子那里更改父母 state 的解决方案，但我没有找到解决方案

可以用ref解决吗？？ （我的计时器组件是一个功能组件）

Answer 1

React ref 转发是解决方案：这个博客将描述更多： https://medium.com/javascript-in-plain-english/react-refs-both-class-and-functional-components-76b7bce487b8

import React, { useState } from "react";
import "./styles.css";

class ChildClass extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      timer: 100
    };
    this.resetTimer = this.resetTimer.bind(this);
  }
  resetTimer() {
    this.setState({
      timer: 0
    });
  }
  render() {
    let { timer } = this.state;
    return <span>{timer}</span>;
  }
}

const ChildFunction = React.forwardRef((props, ref) => {
  const [timer, setTimer] = useState(100);
  const resetTimer = () => {
    setTimer(0);
  };
  React.useImperativeHandle(ref, ()=>({
    resetTimer
  }));
  return <span>{timer}</span>;
});

export default function App() {
  let childClassRef = React.createRef(null);
  let childFuncRef = React.createRef(null);
  const resetClassTimer = () => {
    childClassRef.current.resetTimer();
  };
  const resetFuncTimer = () => {
    childFuncRef.current.resetTimer();
  };
  return (
    <div className="App">
      <ChildClass ref={childClassRef} />
      <button onClick={resetClassTimer}>Reset</button>
      <br/>
      <ChildFunction ref={childFuncRef} />
      <button onClick={resetFuncTimer}>Reset</button>
    </div>
  );
}

我添加了带有 class 组件和功能组件的 ref 转发。 React.js 和 React native 都是一样的。

Answer 2

您所要做的就是将道具传递给孩子，让父母更新 state

  cont Parent = (props) =>{

  const [timer, setTimer] = useState(100)

   cont resetTimer = () => {
      setTimer(0)
   }
   render(){
        return <span>{timer}</span>
        <Child timer={timer}>
      }
}

在孩子

cont Child = (props) =>{
      const timer= props.timer;
      render(){
        return <span>I am child with time {timer}</span>
      }
  }

Answer 3

一种方法是，如果你想从子组件更改父 state 那么你应该通过道具从子组件调用父 function

cont Child = (props) =>{
      render(){
        return (<span>I am child with time {props.timer}</span>
        <Button onClick = {props.resetTimer}></Button>
        )
      }
  }

cont Parent = (props) =>{

  const [timer, setTimer] = useState(100)

   cont resetTimer = () => {
      setTimer(0)
   }
   render(){
        return <span>{timer}</span>
        <Child timer={timer} setTimer={setTimer}>
      }
}