在React上构造数据时遇到问题

import React, { useState, useEffect } from 'react';

function MyComponent() {
  const [data, setData] = useState(null);

  useEffect(() => {
    fetchData();
    return () => {
      // 清理副作用
    };
  }, []);

  const fetchData = async () => {
    const response = await fetch('https://api.example.com/data');
    const result = await response.json();
    setData(result);
  };

  if (!data) {
    return <div>Loading...</div>;
  }

  return (
    <div>
      {data.map(item => (
        <div key={item.id}>{item.name}</div>
      ))}
    </div>
  );
}

import React, { useState, useEffect } from 'react';

function MyComponent() {
  const [data, setData] = useState([]);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    const fetchData = async () => {
      const response = await fetch('https://api.example.com/data');
      const result = await response.json();
      setData(result);
      setLoading(false);
    };

    fetchData();
  }, []);

  if (loading) {
    return <div>Loading...</div>;
  }

  return (
    <div>
      {data.map(item => (
        <div key={item.id}>{item.name}</div>
      ))}
    </div>
  );
}

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

const MyContext = createContext();

function MyProvider({ children }) {
  const [data, setData] = useState('Hello World');

  return (
    <MyContext.Provider value={data}>
      {children}
    </MyContext.Provider>
  );
}

function MyComponent() {
  const data = useContext(MyContext);

  return <div>{data}</div>;
}

function App() {
  return (
    <MyProvider>
      <MyComponent />
    </MyProvider>
  );
}

// actions.js
export const fetchData = () => async dispatch => {
  dispatch({ type: 'FETCH_DATA_REQUEST' });
  try {
    const response = await fetch('https://api.example.com/data');
    const result = await response.json();
    dispatch({ type: 'FETCH_DATA_SUCCESS', payload: result });
  } catch (error) {
    dispatch({ type: 'FETCH_DATA_FAILURE', error });
  }
};

// reducer.js
const initialState = {
  data: [],
  loading: false,
  error: null
};

const dataReducer = (state = initialState, action) => {
  switch (action.type) {
    case 'FETCH_DATA_REQUEST':
      return { ...state, loading: true };
    case 'FETCH_DATA_SUCCESS':
      return { ...state, loading: false, data: action.payload };
    case 'FETCH_DATA_FAILURE':
      return { ...state, loading: false, error: action.error };
    default:
      return state;
  }
};

export default dataReducer;

// store.js
import { createStore, applyMiddleware } from 'redux';
import thunk from 'redux-thunk';
import dataReducer from './reducer';

const store = createStore(dataReducer, applyMiddleware(thunk));

export default store;