如何在页面加载时调度 redux 操作以在 useEffect 中加载数据

Question

我正在尝试将 redux 集成到现有的 react 应用程序中。我正在学习redux。我正在使用钩子。在互联网上有很多使用类组件的例子。我找不到如何使用功能组件实现此目的的示例。

下面的代码不会抛出错误。但是，useEffect 内部的动作没有被调用。该代码不产生任何输出。我想知道电话是否正确。有什么帮助吗？

Index.js

const store = createStore(rubricReducer, applyMiddleware(thunk));     
ReactDOM.render(
    <BrowserRouter basename={baseUrl}>
        <Provider store={store} > <App /> </Provider>
        </BrowserRouter>,
    rootElement);

Rubrics.tsx

const mapStateToProps = state => ({
    rubrics: state.rubrics.items,
    loading: state.rubrics.loading,
    error: state.rubrics.error
});

const mapDispatchToProps = (dispatch) => {
    return {
        getRubrics: () => dispatch(fetchRubrics())
    };
}

const Rubrics = (props) => {    
    const { rubrics, loading, error } = props;

    useEffect(() => {
        props.dispatch(fetchRubrics());
    }, []);    

    if (error) { return <div>Error! {error.message}</div>; }    
    if (loading) { return <div>Loading...</div>; }    

    return (    
        <ul>
            <React.Fragment>
                {rubrics.map(rubric => {
                        return (
                            <li key={rubric.id}>{rubric.title}</li>

                        );
                    })}
            </React.Fragment>
        </ul>
    )
}

export default connect(mapStateToProps, mapDispatchToProps)(Rubrics);

rubricActions.tsx：

export function fetchRubrics() {
    return dispatch => {
        dispatch(fetchRubricsBegin());

        axios.get("api/Rubric/Index")
            .then(response => {
                console.log('success: reading rubrics');

                dispatch(fetchRubricsSuccess(response.data));
                return response.data;
            })
            .catch(error => { fetchRubricsFailure(error) });
    };
}

export const FETCH_RUBRICS_BEGIN = "FETCH_RUBRICS_BEGIN";
export const FETCH_RUBRICS_SUCCESS = "FETCH_RUBRICS_SUCCESS";
export const FETCH_RUBRICS_FAILURE = "FETCH_RUBRICS_FAILURE";

const fetchRubricsBegin = () => ({
    type: FETCH_RUBRICS_BEGIN
})

const fetchRubricsSuccess= (rubrics) => ({
    type: FETCH_RUBRICS_SUCCESS,
    payload: { rubrics}
})


const fetchRubricsFailure = (error) => ({
    type: FETCH_RUBRICS_FAILURE,
    payload: {error}
})

rubricReducer.tsx：

import {
    FETCH_RUBRICS_BEGIN,
    FETCH_RUBRICS_SUCCESS,
    FETCH_RUBRICS_FAILURE
} from '../_actions/rubricActions';

const initialState = {
    rubrics: [],
    loading: false,
    error: null
};

const rubricReducer = (state = initialState, action) => {
    switch (action.type) {
        case FETCH_RUBRICS_BEGIN:
            return {
                ...state,
                loading: true,
                error: null
            };

        case FETCH_RUBRICS_SUCCESS:
            return {
                ...state,
                loading: false,
                items: action.payload.rubrics
            }
        case FETCH_RUBRICS_FAILURE:
            return {
                ...state,
                loading: false,
                error: action.payload.error,
                items: []
            };
        default:
            return state;
    }
}
export default rubricReducer;

Answer 1

在您的调度映射中，您有

const mapDispatchToProps = (dispatch) => {
    return {
        getRubrics: () => dispatch(fetchRubrics())
    };
}

所以不要调用props.dispatch(fetchRubrics()); 只需调用props.getRubrics() 或从道具中解构此方法

const { rubrics, loading, error, getRubrics } = props;

只需拨打getRubrics()

Answer 2

下面是正确的代码：

const Rubrics = (props) => {

    useEffect(() => {
        props.fetchAllRubrics();
    }, [])


    return (
        props.rubrics.map((rubric) => {
            return (<RubricCard rubric={rubric} />)
        })
    )
}

const mapStateToProps = state => ({
    error: state.error,
    rubrics: state.rubrics,
    loading: state.oading
})

const mapDispatchToProps = dispatch => {
    return { fetchAllRubrics: () => dispatch(fetchRubricsData()) }
}

export default connect(
    mapStateToProps,
    mapDispatchToProps
)(Rubrics);

Answer 3

这里的问题是您使用了不正确的 mapDispatchToProps。你不需要显式设置 dispatch 函数，这就是 react redux 为你做的。

所以，下面是正确的做法：

// Now you won't be creating a new object every time your component re-renders
const mapDispatchToProps = {
  getRubrics: fetchRubrics
}

const Rubrics = (props) => {    
  const { getRubrics } = props;

  // You should always add elements inside your render scope
  // to the second array parameter of useEffect to prevent unexpected bugs.
  useEffect(() => {
      getRubrics();
  }, [getRubrics]);

  return (    
    <div>Your component here!</div>
  )
}

Answer 4

使用自 v7.1.0 起由react-redux 提供的hooks，现在可以在没有mapStateToProps 和mapDispatchToProps 的情况下编写。

import React, { useEffect } from 'react';
import { useDispatch, useSelector } from 'react-redux';


const Rubrics = () => {
  const dispatch = useDispatch();

  const { rubrics, loading, error } = useSelector(
    state => ({
      error: state.error,
      rubrics: state.rubrics,
      loading: state.loading
    })
  );

  useEffect(() => {
    dispatch(fetchRubrics());
  }, [dispatch]);

  if (error) { return <div>Error! {error.message}</div>; }
  if (loading) { return <div>Loading...</div>; }

  return (
    <ul>
      <React.Fragment>
        {rubrics.map(rubric => {
          return (
            <li key={rubric.id}>{rubric.title}</li>
          );
        })}
      </React.Fragment>
    </ul>
  )
};