【React】实现类似vue的keepAlive组件的持久化

1. 创建 KeepAliveContext.js

首先，我们需要创建一个 KeepAliveContext 来存储需要持久化的组件实例。

// src/KeepAliveContext.js
import { createContext, useState } from "react"

export const KeepAliveContext = createContext()

function KeepAliveProvider(props) {
  /**
   * {
   *   home: {
   *      id: 'home',
   *      element: element,
   *      nodes: nodes,
   *   },
   *   user: {
   *      id: 'user',
   *      element: element,
   *      nodes: nodes,
   *   }
   * }
   */
  const [cached, setCached] = useState({})

  return (
    <KeepAliveContext.Provider value={{ cached, setCached }}>
      {props.children}
      {Object.values(cached).map(({ id, element, nodes }) => (
        <div
          key={id}
          ref={(node) => {
            if (node && !nodes) {
              // 缓存实例的 childNodes
              setCached({
                ...cached,
                [id]: { id, element, nodes: [...node.childNodes] }
              })
            }
          }}
        >
          {element}
        </div>
      ))}
    </KeepAliveContext.Provider>
  )
}

export default KeepAliveProvider

2. 创建 keepAlive.js

接下来，我们创建 keepAlive 函数，该函数负责缓存组件的实例。

// src/KeepAlive.js
/* eslint-disable react-hooks/rules-of-hooks */
import { useContext, useEffect, useRef } from "react"
import { KeepAliveContext } from "./KeepAliveContext"

export default function KeepAlive(KeepAliveComponent, id) {
  return function (props) {
    const _ref = useRef(null)
    const { cached, setCached } = useContext(KeepAliveContext)
    useEffect(() => {
      if (!cached[id]) {
        // 首次初始化时缓存组件实例
        setCached({
          ...cached,
          [id]: { id, element: <KeepAliveComponent {...props} />, nodes: null }
        })
      } else {
        const { nodes } = cached[id]
        if (nodes && Array.isArray(nodes)) {
          nodes.forEach((node) => _ref.current.appendChild(node))
        }
      }
    }, [cached, setCached, props])
    return <div ref={_ref}></div>
  }
}

3. 创建示例组件 Counter.js

这是一个简单的计数器组件，用于测试 KeepAlive 功能。

// src/components/Counter.js
import React, { useState } from 'react';

const Counter = () => {
  const [count, setCount] = useState(0);

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
};

export default Counter;

4. 创建应用主组件 App.js

在这个主组件中，我们使用 KeepAliveProvider 和 keepAlive 函数来管理组件的持久化。

// src/App.js
import React, { useState } from 'react';
import { KeepAliveProvider } from './KeepAliveContext';
import keepAlive from './keepAlive';
import Counter from './components/Counter';

const AliveCounter = keepAlive('counter', Counter);

const App = () => {
  const [showCounter, setShowCounter] = useState(true);

  return (
    <KeepAliveProvider>
      <div>
        <button onClick={() => setShowCounter(!showCounter)}>
          {showCounter ? 'Hide' : 'Show'} Counter
        </button>
        {showCounter && <AliveCounter />}
      </div>
    </KeepAliveProvider>
  );
};

export default App;

5. 入口文件 index.js

确保在你的入口文件中正确引入 App 组件并渲染它。

// src/index.js
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById('root')
);

总结

通过这个完整的案例，我们实现了一个类似于 Vue 的 KeepAlive 功能的组件，通过缓存组件的实例和其 childNodes，在重新渲染时通过读取childNodes恢复组件。通过这种方式，我们可以确保组件的实际 DOM 节点在卸载和重新挂载之间保持不变，从而实现了组件的持久化。