React useCallback with debounce 适用于旧值，如何获取实际状态值？

Question

我无法满足所有条件：

1. 我需要内部的一些函数useCallback，因为我将它设置为子组件的道具（用于防止重新渲染）
2. 我需要使用debounce，因为我的函数是“终点”，可以调用 ~100 次/秒
3. 我需要在去抖动后获取当前（实际值）。

我对最后一点有问题，我在去抖动（1000 毫秒）后的值已过时。

如何使用useCallback+获取当前值debounce？（警报中的值必须与页面相同）

//ES6 const, let
//ES6 Destructuring 
const { Component, useCallback, useState, useEffect } = React;

const SUBChildComponent = (props) => (<button onClick={props.getVal}>GetValue with debounce</button>);

const ChildComponent = () => {
    // some unstable states
    const [someVal1, setSomeVal1] = useState(0);
    const [someVal2, setSomeVal2] = useState(0);
    const [someVal3, setSomeVal3] = useState(0);

    // some callback witch works with states AND called from subClild components
    const getVal = useCallback(_.debounce(() => {
        alert(`${someVal1}\n${someVal2}\n${someVal3}`);
    }, 1000), [someVal1, someVal2, someVal3]);

    // some synthetic changes
    useEffect(() => {
        const id = setInterval(() => setSomeVal1(someVal1 + 1), 50);
        return () => clearInterval(id);
    }, [someVal1]);

    // some synthetic changes
    useEffect(() => {
        const id = setInterval(() => setSomeVal2(someVal2 + 1), 100);
        return () => clearInterval(id);
    }, [someVal2]);

    // some synthetic changes
    useEffect(() => {
        const id = setInterval(() => setSomeVal3(someVal3 + 1), 250);
        return () => clearInterval(id);
    }, [someVal3]);

    return <React.Fragment><SUBChildComponent getVal={getVal}/><br/>{someVal1}<br/>{someVal2}<br/>{someVal3}
    </React.Fragment>;
};

class App extends Component {
    render() {
        return (<div><ChildComponent/></div>);
    }
}

ReactDOM.render(<App/>, document.querySelector(".container"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.6/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.6/umd/react-dom.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.5.0/lodash.min.js"></script>

<div class="container"></div>

Answer 1

首先，您必须注意 debounce 函数在其创建时从其闭包中设置状态。现在该函数在几秒钟后执行，到那时状态会发生变化。每次更新状态时都会创建一个新的 debounce 实例，因此如果您完全使用 debounce 函数 onClick，它将无法正常工作，因为不同的调用将调用不同的 debounce 函数实例而不是同一个

在这种情况下的解决方案是将状态值作为参数传递给 debounce 函数，而不是让它依赖于闭包。但是它仍然使用调用 debounce 的值，如下面的代码片段所示

//ES6 const, let
//ES6 Destructuring 
const { Component, useCallback, useState, useEffect } = React;

const SUBChildComponent = ({getVal, someVal1,someVal2,someVal3}) => (<button onClick={() => getVal(someVal1,someVal2,someVal3)}>GetValue with debounce</button>);

const ChildComponent = () => {
    // some unstable states
    const [someVal1, setSomeVal1] = useState(0);
    const [someVal2, setSomeVal2] = useState(0);
    const [someVal3, setSomeVal3] = useState(0);

    // some callback witch works with states AND called from subClild components
    const getVal = useCallback(_.debounce((val1, val2, val3) => {
        alert(`${val1}\n${val2}\n${val3}`);
    }, 1000), []); // create debounce function only once

    // some synthetic changes
    useEffect(() => {
        const id = setInterval(() => setSomeVal1(someVal1 + 1), 50);
        return () => clearInterval(id);
    }, [someVal1]);

    // some synthetic changes
    useEffect(() => {
        const id = setInterval(() => setSomeVal2(someVal2 + 1), 100);
        return () => clearInterval(id);
    }, [someVal2]);

    // some synthetic changes
    useEffect(() => {
        const id = setInterval(() => setSomeVal3(someVal3 + 1), 250);
        return () => clearInterval(id);
    }, [someVal3]);

    return <React.Fragment><SUBChildComponent someVal1={someVal1} someVal2={someVal2} someVal3={someVal3} getVal={getVal}/><br/>{someVal1}<br/>{someVal2}<br/>{someVal3}
    </React.Fragment>;
};

class App extends Component {
    render() {
        return (<div><ChildComponent/></div>);
    }
}

ReactDOM.render(<App/>, document.querySelector(".container"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.6/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.6/umd/react-dom.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.5.0/lodash.min.js"></script>

<div class="container"></div>

现在另一个解决方案是保留状态引用并在 debounce 函数中使用它们，这正是您想要的

//ES6 const, let
//ES6 Destructuring 
const { Component, useCallback, useState, useEffect, useRef } = React;

const SUBChildComponent = React.memo(({getVal}) => {
    console.log('child render');
    return <button onClick={() => getVal()}>GetValue with debounce</button>;
});

const ChildComponent = () => {
    // some unstable states
    const [someVal1, setSomeVal1] = useState(0);
    const [someVal2, setSomeVal2] = useState(0);
    const [someVal3, setSomeVal3] = useState(0);
    const someVal1Ref = useRef(someVal1);
    const someVal2Ref = useRef(someVal2);
    const someVal3Ref = useRef(someVal3);
     
    useEffect(() => {
        someVal1Ref.current = someVal1;
        someVal2Ref.current = someVal2;
        someVal3Ref.current = someVal3;
    }, [someVal1, someVal2, someVal3])
    
    // some callback witch works with states AND called from subClild components
    const getVal = useCallback(_.debounce(() => {
        alert(`${someVal1Ref.current}\n${someVal2Ref.current}\n${someVal3Ref.current}`);
    }, 1000), []); // create debounce function only once

    // some synthetic changes
    useEffect(() => {
        const id = setInterval(() => setSomeVal1(someVal1 + 1), 50);
        return () => clearInterval(id);
    }, [someVal1]);

    // some synthetic changes
    useEffect(() => {
        const id = setInterval(() => setSomeVal2(someVal2 + 1), 100);
        return () => clearInterval(id);
    }, [someVal2]);

    // some synthetic changes
    useEffect(() => {
        const id = setInterval(() => setSomeVal3(someVal3 + 1), 250);
        return () => clearInterval(id);
    }, [someVal3]);

    return <React.Fragment><SUBChildComponent getVal={getVal}/><br/>{someVal1}<br/>{someVal2}<br/>{someVal3}
    </React.Fragment>;
};

class App extends Component {
    render() {
        return (<div><ChildComponent/></div>);
    }
}

ReactDOM.render(<App/>, document.querySelector(".container"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.6/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.6/umd/react-dom.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.5.0/lodash.min.js"></script>

<div class="container"></div>

附注。这种实现在类组件中更容易，并且不需要任何解决方法，因为您不依赖于闭包