React Hooks中的useContext和useReducer如何結合使用

在React Hooks中，可以結合使用useContext和useReducer來實現全局狀態管理。useContext用于獲取全局狀態，而useReducer用于更新全局狀態。

首先，可以創建一個Context對象來存儲全局狀態和dispatch函數：

import React, { createContext, useContext, useReducer } from 'react';

const initialState = {
  count: 0,
};

const reducer = (state, action) => {
  switch(action.type) {
    case 'INCREMENT':
      return { count: state.count + 1 };
    case 'DECREMENT':
      return { count: state.count - 1 };
    default:
      return state;
  }
};

const GlobalContext = createContext();

const GlobalProvider = ({ children }) => {
  const [state, dispatch] = useReducer(reducer, initialState);

  return (
    <GlobalContext.Provider value={{ state, dispatch }}>
      {children}
    </GlobalContext.Provider>
  );
};

const useGlobalContext = () => {
  return useContext(GlobalContext);
};

export { GlobalProvider, useGlobalContext };

然后，在組件中使用useGlobalContext來獲取全局狀態和dispatch函數：

import React from 'react';
import { useGlobalContext } from './GlobalContext';

const Counter = () => {
  const { state, dispatch } = useGlobalContext();

  const handleIncrement = () => {
    dispatch({ type: 'INCREMENT' });
  };

  const handleDecrement = () => {
    dispatch({ type: 'DECREMENT' });
  };

  return (
    <div>
      <h1>Count: {state.count}</h1>
      <button onClick={handleIncrement}>Increment</button>
      <button onClick={handleDecrement}>Decrement</button>
    </div>
  );
};

export default Counter;

這樣就可以在整個應用中共享狀態，并且通過dispatch函數來更新全局狀態。