如何在反应中使用带有useState钩子的回调[重复]

Question

我正在使用带有钩子的功能组件。我需要从孩子更新父母的状态。我在 Parent 中使用了一个 prop 函数。 一切正常，除了我的 prop 函数正在获取以前的状态而不是当前状态。我的 prop 函数在 useState 钩子设置当前状态之前执行。 我怎样才能等待我的回调函数在 useState 调用后执行。我正在从基于类的组件中寻找类似 setState(state,callback) 的东西。

这里是sn-p的代码：

function Parent() {
  const [Name, setName] = useState("");
  getChildChange = getChildChange.bind(this);
  function getChildChange(value) {
    setName(value);
  }

  return <div> {Name} :
    <Child getChildChange={getChildChange} ></Child>
  </div>
}

function Child(props) {
  const [Name, setName] = useState("");
  handleChange = handleChange.bind(this);

  function handleChange(ele) {
    setName(ele.target.value);
    props.getChildChange(collectState());
  }

  function collectState() {
    return Name;
  }

  return (<div>
    <input onChange={handleChange} value={Name}></input>
  </div>);
} 

Answer 1

对于 React16.x 及更高版本，如果您想使用 useState 挂钩在状态更改时调用回调函数，您可以使用附加到状态更改的 useEffect 挂钩。

import React, { useEffect } from "react";

useEffect(() => {
  props.getChildChange(name); // using camelCase for variable name is recommended.
}, [name]); // this will call getChildChange when ever name changes.

Answer 2

setState(updater, callback) 为useState

以下实现非常接近于类的原始setState 回调。

对accepted answer的改进：

1. 在初始渲染时省略了回调执行 - 我们只想在状态 updates 时调用它
2. 每个 setState 调用的回调可以是动态的，就像类一样

用法

const App = () => {
  const [state, setState] = useStateCallback(0); // same API as useState

  const handleClick = () => {
    setState(
      prev => prev + 1,
      // second argument is callback, `s` being the *updated* state
      s => console.log("I am called after setState, state:", s)
    );
  };

  return <button onClick={handleClick}>Increment</button>;
}

useStateCallback

function useStateCallback(initialState) {
  const [state, setState] = useState(initialState);
  const cbRef = useRef(null); // init mutable ref container for callbacks

  const setStateCallback = useCallback((state, cb) => {
    cbRef.current = cb; // store current, passed callback in ref
    setState(state);
  }, []); // keep object reference stable, exactly like `useState`

  useEffect(() => {
    // cb.current is `null` on initial render, 
    // so we only invoke callback on state *updates*
    if (cbRef.current) {
      cbRef.current(state);
      cbRef.current = null; // reset callback after execution
    }
  }, [state]);

  return [state, setStateCallback];
}

更多信息：React Hooks FAQ: Is there something like instance variables?

工作示例

const App = () => {
  const [state, setState] = useStateCallback(0);

  const handleClick = () =>
    setState(
      prev => prev + 1,
      // important: use `s`, not the stale/old closure value `state`
      s => console.log("I am called after setState, state:", s)
    );

  return (
    <div>
      <p>Hello Comp. State: {state} </p>
      <button onClick={handleClick}>Click me</button>
    </div>
  );
}

function useStateCallback(initialState) {
  const [state, setState] = useState(initialState);
  const cbRef = useRef(null);

  const setStateCallback = useCallback((state, cb) => {
    cbRef.current = cb; 
    setState(state);
  }, []);

  useEffect(() => {
    if (cbRef.current) {
      cbRef.current(state);
      cbRef.current = null;
    }
  }, [state]);

  return [state, setStateCallback];
}

ReactDOM.render(<App />, document.getElementById("root"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<script>var { useReducer, useEffect, useState, useRef, useCallback } = React</script>
<div id="root"></div>

Answer 3

您可以使用useCallback 挂钩来执行此操作。

function Parent() {
  const [name, setName] = useState("");
  const getChildChange = useCallback( (updatedName) => {
    setName(updatedName);
  }, []);

  return <div> {name} :
    <Child getChildChange={getChildChange} ></Child>
  </div>
}

function Child(props) {
  const [name, setName] = useState("");

  function handleChange(ele) {
    setName(ele.target.value);
    props.getChildChange(ele.target.value);
  }

  function collectState() {
    return name;
  }

  return (<div>
    <input onChange={handleChange} value={name}></input>
  </div>);
}

Answer 4

实现此目的的另一种方法：

const [Name, setName] = useState({val:"", callback: null});
React.useEffect(()=>{
  console.log(Name)
  const {callback} = Name;
  callback && callback();
}, [Name]);
setName({val:'foo', callback: ()=>setName({val: 'then bar'})})

Answer 5

您可以使用 useEffect/useLayoutEffect 来实现：

const SomeComponent = () => {
  const [count, setCount] = React.useState(0)

  React.useEffect(() => {
    if (count > 1) {
      document.title = 'Threshold of over 1 reached.';
    } else {
      document.title = 'No threshold reached.';
    }
  }, [count]);

  return (
    <div>
      <p>{count}</p>

      <button type="button" onClick={() => setCount(count + 1)}>
        Increase
      </button>
    </div>
  );
};

更多信息请关注here。

如果您正在寻找开箱即用的解决方案，请查看 this custom hook，它的工作方式与 useState 类似，但接受回调函数作为第二个参数：

// npm install use-state-with-callback

import useStateWithCallback from 'use-state-with-callback';

const SomeOtherComponent = () => {
  const [count, setCount] = useStateWithCallback(0, count => {
    if (count > 1) {
      document.title = 'Threshold of over 1 reached.';
    } else {
      document.title = 'No threshold reached.';
    }
  });

  return (
    <div>
      <p>{count}</p>

      <button type="button" onClick={() => setCount(count + 1)}>
        Increase
      </button>
    </div>
  );
};

Answer 6

我们可以编写自定义函数，如果状态发生任何变化，它将调用回调函数

import React, { useState, useEffect } from "react";
import ReactDOM from "react-dom";

import "./styles.css";

const useStateCallbackWrapper = (initilValue, callBack) => {
  const [state, setState] = useState(initilValue);
  useEffect(() => callBack(state), [state]);
  return [state, setState];
};

const callBack = state => {
  console.log("---------------", state);
};
function App() {
  const [count, setCount] = useStateCallbackWrapper(0, callBack);
  return (
    <div className="App">
      <h1>{count}</h1>
      <button onClick={() => setCount(count + 1)}>+</button>
      <h2>Start editing to see some magic happen!</h2>
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

`

Answer 7

其实在使用 react hooks 的时候应该避免使用this。它会引起副作用。这就是为什么反应团队创建react hooks。

如果您删除试图绑定this 的代码，您只需将Parent 中的setName 传递给Child 并在handleChange 中调用它。更简洁的代码！

function Parent() {
  const [Name, setName] = useState("");

  return <div> {Name} :
    <Child setName={setName} ></Child>
  </div>
}

function Child(props) {
  const [Name, setName] = useState("");

  function handleChange(ele) {
    setName(ele.target.value);
    props.setName(ele.target.value);
  }

  return (<div>
    <input onChange={handleChange} value={Name}></input>
  </div>);
} 

此外，您不必创建两个Name 的副本（一个在Parent 中，另一个在Child 中）。坚持“单一真理来源”原则，Child 不必拥有状态Name，而是从Parent 接收它。更干净的节点！

function Parent() {
  const [Name, setName] = useState("");

  return <div> {Name} :
    <Child setName={setName} Name={Name}></Child>
  </div>
}

function Child(props) {    
  function handleChange(ele) {
    props.setName(ele.target.value);
  }

  return (<div>
    <input onChange={handleChange} value={props.Name}></input>
  </div>);
} 

Answer 8

你可以像下面这样使用 -

this.setState(() => ({  subChartType1: value   }), () => this.props.dispatch(setChartData(null)));

Answer 9

function Parent() {
  const [Name, setName] = useState("");
  getChildChange = getChildChange.bind(this);
  function getChildChange(value) {
    setName(value);
  }

  return <div> {Name} :
    <Child getChildChange={getChildChange} ></Child>
  </div>
}

function Child(props) {
  const [Name, setName] = useState("");
  handleChange = handleChange.bind(this);
  collectState = collectState.bind(this);
  
  function handleChange(ele) {
    setName(ele.target.value);
  }

  function collectState() {
    return Name;
  }
  
   useEffect(() => {
    props.getChildChange(collectState());
   });

  return (<div>
    <input onChange={handleChange} value={Name}></input>
  </div>);
} 

useEffect充当componentDidMount，componentDidUpdate，所以在更新状态后会起作用