如何使用React的Context API實現跨組件狀態共享

要使用React的Context API實現跨組件狀態共享，首先需要創建一個包含共享狀態的上下文對象。然后，將這個上下文對象提供給所有需要訪問共享狀態的組件。

以下是一個簡單的示例：

1. 創建一個包含共享狀態的上下文對象

// SharedStateContext.js
import React, { createContext, useState } from 'react';

const SharedStateContext = createContext();

const SharedStateProvider = ({ children }) => {
  const [sharedState, setSharedState] = useState('');

  return (
    <SharedStateContext.Provider value={{ sharedState, setSharedState }}>
      {children}
    </SharedStateContext.Provider>
  );
};

export { SharedStateContext, SharedStateProvider };

2. 在根組件中使用SharedStateProvider提供上下文

// App.js
import React from 'react';
import { SharedStateProvider } from './SharedStateContext';
import ComponentA from './ComponentA';
import ComponentB from './ComponentB';

const App = () => {
  return (
    <SharedStateProvider>
      <ComponentA />
      <ComponentB />
    </SharedStateProvider>
  );
};

export default App;

3. 在需要訪問共享狀態的組件中使用SharedStateContext.Consumer

// ComponentA.js
import React, { useContext } from 'react';
import { SharedStateContext } from './SharedStateContext';

const ComponentA = () => {
  const { sharedState, setSharedState } = useContext(SharedStateContext);

  return (
    <div>
      <h1>Component A</h1>
      <p>Shared state: {sharedState}</p>
      <button onClick={() => setSharedState('Hello from Component A')}>Update State</button>
    </div>
  );
};

export default ComponentA;

// ComponentB.js
import React, { useContext } from 'react';
import { SharedStateContext } from './SharedStateContext';

const ComponentB = () => {
  const { sharedState, setSharedState } = useContext(SharedStateContext);

  return (
    <div>
      <h1>Component B</h1>
      <p>Shared state: {sharedState}</p>
      <button onClick={() => setSharedState('Hello from Component B')}>Update State</button>
    </div>
  );
};

export default ComponentB;

通過以上步驟，就可以在ComponentA和ComponentB中共享狀態，并且在一個組件中更新狀態后，另一個組件也會同步更新。