React Hooks - useState 值不能改变

Question

问题

我想在每次单击 enter 时获取更新挂钩状态的 value。但我总是得到初始值，而不是更新后的值。

代码

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

const ItemCol = props => {
  const [value, setValue] = useState("Initial Value");

  const onChange = event => {
    setValue(event.target.value);
    console.log("onChange: " + value);
  };

  const keyDown = event => {
    if (event.keyCode === 13) {
      event.preventDefault();
      //Value should be changed, but did not change
      console.log("Enter Pressed: " + value);
    }
  };

  return (
    <ContentEditable
      html={value}
      onKeyDown={React.useCallback(keyDown)}
      onChange={React.useCallback(onChange)}
    />
  );
};

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

CodeSandBox.io: https://codesandbox.io/embed/pensive-worker-31l3r

注意：keyCode 13 是 Enter。

注意 2：我正在使用 react-contenteditable 依赖项。 (https://www.npmjs.com/package/react-contenteditable)

请帮帮我，因为这个问题困扰我好几个小时了。谢谢！

Answer 1

ContentEditable 组件似乎记住了 onKeydown 方法，因此每当您调用它时，它都会打印其初始闭包中的值，这就是为什么您始终拥有初始值的原因。

要解决这个闭包问题，您可以将值保留在 ref 中并对其进行修改

const ItemCol = props => {
  const [value, setValue] = useState("Initial Value");
  const valRef = useRef(value);
  const onChange = event => {
    setValue(event.target.value);
    valRef.current = event.target.value;
  };

  const keyDown = event => {
    if (event.keyCode === 13) {
      event.preventDefault();
      //Value should be changed, but did not change
      console.log("Enter Pressed: " + valRef.current);
    }
  };

  return (
    <ContentEditable
      html={value}
      onKeyDown={keyDown}
      onChange={React.useCallback(onChange)}
    />
  );
};

Working demo

Answer 2

@Michael Harley，问题出在闭包或 react-content-editable onkeydown 函数设置方式 react-content-editable.

工作演示：- https://codesandbox.io/embed/elated-bohr-jeu4u?fontsize=14

资源：- https://overreacted.io/a-complete-guide-to-useeffect/

React Hooks - useState 值不能改变

React Hooks - useState value cannot change

contenteditable

reactjs

react-hooks