React 中的 useCallback 似乎不允许我更新父级中的状态

Question

我创建了一个简单示例，说明 useCallback 如何不允许我保留状态更改。当我删除 useCallback 时，我存储在状态中的计数器会按预期更新，但是添加 useCallback（我希望它会保留所有扬声器项目的重新渲染而不是重新渲染）会不断将我的状态重置为原始状态 (0,0 ,0).

问题代码在codesandbox中：

https://codesandbox.io/s/flamboyant-shaw-2wtqj?file=/pages/index.js

这里是实际的简单文件示例

import React, { useState, memo, useCallback } from 'react';

const Speaker = memo(({ speaker, speakerClick }) => {
  console.log(speaker.id)
  return (
    <div>
      <span
        onClick={() => {
          speakerClick(speaker.id);
        }}
        src={`speakerimages/Speaker-${speaker.id}.jpg`}
        width={100}
      >{speaker.id} {speaker.name}</span>
      &nbsp;&nbsp;
      <span className="fa fa-star ">&nbsp;&nbsp;{speaker.clickCount}</span>
      &nbsp;
    </div>
  );
});

function SpeakerList({ speakers, setSpeakers }) {
  return (
    <div>
      {speakers.map((speaker) => {
        return (
          <Speaker
            speaker={speaker}
            speakerClick={useCallback((id) => {
              const speakersNew = speakers.map((speaker) => {
                return speaker.id === id
                    ? { ...speaker, clickCount: speaker.clickCount + 1 }
                    : speaker;
              });
              setSpeakers(speakersNew);
            },[])}
            key={speaker.id}
          />
        );
      })}
    </div>
  );
}

//
const App = () => {
  const speakersArray = [
    { id: 1124, name: 'aaa', clickCount: 0 },
    { id: 1530, name: 'bbb', clickCount: 0 },
    { id: 10803, name: 'ccc', clickCount: 0 },
  ];

  const [speakers, setSpeakers] = useState(speakersArray);

  return (
    <div>
      <h1>Speaker List</h1>
      <SpeakerList speakers={speakers} setSpeakers={setSpeakers}></SpeakerList>
    </div>
  );
};
export default App;

Answer 1

首先，你只能在组件主体处使用钩子，不能在speakerClick props 函数声明处包裹它。其次，useCallback 将保留原始的 speakers 对象引用，这将是一个过时的值。要解决此问题，您可以使用 setSpeakers 传递回调，您的函数将在当前 speakers 状态下被调用：

function SpeakerList({ speakers, setSpeakers }) {
  const speakerClick = useCallback(
    (id) => {
      // passing a callback avoid using a stale object reference
      setSpeakers((speakers) => {
        return speakers.map((speaker) => {
          return speaker.id === id
            ? { ...speaker, clickCount: speaker.clickCount + 1 }
            : speaker;
        });
      });
    },
    [setSpeakers] // you can add setSpeakers as dependency since it'll remain the same
  );

  return (
    <div>
      {speakers.map((speaker) => {
        return (
          <Speaker
            speaker={speaker}
            speakerClick={speakerClick}
            key={speaker.id}
          />
        );
      })}
    </div>
  );
}

React 中的 useCallback 似乎不允许我更新父级中的状态

useCallback in React seems to be not letting me update state in parent

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