useDispatch() 错误：找不到 react-redux 上下文值；请确保组件被包裹在 <Provider> 中

Question

我正在尝试使用 React-Redux 库，但标题出现错误。我用 Provider 包装了我的组件，但我仍然收到错误，只有当我实现 useDispatch() 钩子时。

该应用程序运行良好，直到我添加了 useDispatch() 行。可以删除有关调度功能的其余行，但我仍然遇到相同的错误。

如果你能帮助我，我将不胜感激。谢谢

这是我的代码：

import 'react-native-gesture-handler';
import {NavigationContainer} from '@react-navigation/native';
import Navigator from './navigation/Navigator';

import React, {useEffect, useState, useCallback} from 'react';
import {SafeAreaView, StyleSheet, Text, View} from 'react-native';

import {createStore, combineReducers} from 'redux';
import {Provider, useDispatch} from 'react-redux';
import dataReducer from './store/reducers/dataReducer';
import {CONSTANTS} from './constants/constants';
import {saveInitialData} from './store/actions/dataActions';

const App = () => {
  const [fetched, setFetched] = useState(initialState);

  const dispatch = useDispatch();

  const saveInitialDataHandler = useCallback(data => {
    dispatch(saveInitialData(data));
    callback;
  }, []);

  const rootReducer = combineReducers({
    content: dataReducer,
  });

  const store = createStore(rootReducer);

  useEffect(() => {
    fetchData();
  }, []);

  const fetchData = () => {
    fetch(CONSTANTS.database)
      .then(response => response.json())
      .then(responseJSON => {
        setFetched(true);
        saveInitialDataHandler(responseJSON);
      });
  };

  if (!fetched) {
    return (
      <Provider store={store}>
        <View stlye={{flex: 1, alignItems: 'center', justifyContent: 'center'}}>
          <Text></Text>
        </View>
      </Provider>
    );
  } else {
    return (
      <Provider store={store}>
        <NavigationContainer>
          <SafeAreaView style={styles.SafeAreaView}>
            <Navigator></Navigator>
          </SafeAreaView>
        </NavigationContainer>
      </Provider>
    );
  }
};

const styles = StyleSheet.create({
  SafeAreaView: {flex: 1},
});

export default App;

Answer 1

App必须包含在 provider 中，因为您正在使用useDispatch它。现在只是个孩子。Provider设置上下文，以便只有它的孩子可以访问它，而不是父母。

一种解决方案是为其创建一个包装器组件：

const AppWrapper = () => {
  const store = createStore(rootReducer);

  return (
    <Provider store={store}> // Set context
      <App /> // Now App has access to context
    </Provider>
  )
}

const App = () => {
  const dispatch = useDispatch(); // Works!
...

Answer 2

如果运行时出现此错误，npm run test则问题与您的测试文件有关。

app.test.tsx用下面的代码更新或替换您的

redux-mock-store注意：如果您还没有安装，请不要忘记安装。

import React from 'react';
import { render } from '@testing-library/react';

import App from './App';

import { Provider } from 'react-redux';
import configureStore from 'redux-mock-store';

describe('With React Testing Library', () => {
    const initialState = { output: 10 };
    const mockStore = configureStore();
    let store;

    it('Shows "Hello world!"', () => {
        store = mockStore(initialState);
        const { getByText } = render(
            <Provider store={store}>
                <App />
            </Provider>
        );

        expect(getByText('Hello World!')).not.toBeNull();
    });
});

经过 1 个小时的搜索，我得到了这个解决方案。非常感谢OSTE

原始解决方案：Github issues/8145 和解决方案链接

使用此解决方案，如果您收到类似TypeError: window.matchMedia is not a function 的错误，请通过这种方式解决。将这些行添加到您的setupTests.ts文件中。原始解决方案链接stackoverflow.com/a/64872224/5404861

global.matchMedia = global.matchMedia || function () {
  return {
    addListener: jest.fn(),
    removeListener: jest.fn(),
  };
};

Answer 3

也许您将 Provider 导入到 App.js 文件中。Provider需要导入到index.js文件中。

/*index.js*/
import React from 'react';
import ReactDOM from 'react-dom';
import { Provider } from 'react-redux';
import { store } from './store/reduxStore';
import './index.css';
import App from './App';
import reportWebVitals from './reportWebVitals';

ReactDOM.render(
  <React.StrictMode>
    <Provider store={store}>
      <App />
    </Provider>
  </React.StrictMode>,
  document.getElementById('root')
);

Answer 4

我在react-native应用程序的同一个index.js文件上执行了此操作。这样，您就不必导出并添加另一个文件，只是为了向提供商提供应用程序包装。

const ReduxProvider = () => {
    return(
        <Provider store={store}>
            <App />
        </Provider>
    )
}

AppRegistry.registerComponent(appName, () => ReduxProvider);