为什么我的reducer在react / redux中返回一个空数组？

Question

在我的reducer中，它返回我从api获取的对象数组。我在列表上做了一个console.log，我可以看到这个数组，但是当我访问我的react类中的reducer时，它显示为一个空数组，为什么会这样呢？在我的react文件的render（）函数内部，它确实出于某种奇怪的原因而打印，但是我有一个函数试图使用化简器中的数据来渲染单独的div，并且数组显示为空。

getList() {
        let arr = [];
        if(this.props.popular){
            arr = this.props.popular.map(item => {
                return (
                    <div key={item.id} className="movie">
                        <img
                            src={`https://image.tmdb.org/t/p/w300${item.poster_path}`}
                            //onClick={() => this.displayModal(item)}
                        />
                    </div>)
            })
        }
        // console.log(arr)
        // this.props.updateCurrentShowList(arr);
        return arr;
    }

我从下面使用的mapstatetoprops函数中使用this.props.popular。

import { FETCH_POPULAR, RESET_POPULAR } from "../Actions/types";

let initialList = [];

export default function(state = initialList, action){
    switch(action.type){
        case FETCH_POPULAR:
            //return action.payload || false;
            initialList = initialList.concat(...action.payload);
            //console.log(initialList);
            return initialList;

        case RESET_POPULAR:
            initialList = action.payload;
            return initialList;

        default:
            return state;
    }
}

在这里initialList被打印并工作，然后我将其返回。

这是我在要访问该数组的其他文件中拥有的mapStateToProps函数。我在我的reducers文件中使用了Combinereducers。

function mapStateToProps(state) {
    return {
        popular: state.popular
    };
}

为什么在render（）中执行this.props.popular可以正确打印，但是无论何时在其他任何地方使用它，都不会打印？

动作功能

export const fetchPopular = (searchTypeFormat, page) => async (dispatch) => {
    let url = `https://api.themoviedb.org/3/discover/${searchTypeFormat}?api_key=${APIKEY}&language=en-US&sort_by=popularity.desc&include_adult=false&include_video=false&page=${page}`;
    //console.log(url);
    const res = await axios.get(url);
    //console.log(res.data.results)
    dispatch({type: FETCH_POPULAR, payload: res.data.results});
};

我的店铺创作

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
import { Provider } from 'react-redux';
import { createStore, applyMiddleware } from 'redux';
import reducers from './Reducers/index';
import reduxThunk from 'redux-thunk';


const store = createStore(reducers, {}, applyMiddleware(reduxThunk));

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

我这样组合减速机

import { combineReducers } from 'redux';
import authReducer from './authReducer';
import popularReducer from './popularReducer';
import genreListReducer from './genreListReducer';
import searchByGenreReducer from './searchByGenreReducer';
import { reducer as formReducer } from 'redux-form';
import modalReducer from './modalReducer';
import detailsReducer from './moreDetailReducer';
import userDisplayList from './userDisplayList';

export default combineReducers({
    auth: authReducer,
    form: formReducer,
    popular: popularReducer,
    genreList: genreListReducer,
    searchByGenre: searchByGenreReducer,
    modalData: modalReducer,
    details: detailsReducer,
    displayList: userDisplayList
})

整个组成部分

import React, { Component } from 'react';
import { withRouter } from "react-router-dom";
import { connect } from 'react-redux';
import * as actions from '../Actions';

class SearchPopular extends Component {
    constructor(props) {
        super(props);

        this.state = {
            list: [],
            page: 1
        }
        this.getList = this.getList.bind(this);
    }
    componentWillMount() {
        //console.log(this.props.match.params.format)
        this.props.fetchPopular(this.props.match.params.format, this.state.page);
        console.log(this.props.popular)
        console.log(this.getList());
    }

    getList() {
        let arr = [];
        if(this.props.popular){
            arr = this.props.popular.map(item => {
                return (
                    <div key={item.id} className="movie">
                        <img
                            src={`https://image.tmdb.org/t/p/w300${item.poster_path}`}
                            //onClick={() => this.displayModal(item)}
                        />
                    </div>)
            })
        }
        //console.log(arr)
        // this.props.updateCurrentShowList(arr);
        return arr;
    }

render() {
    console.log(this.props.popular);
    return (
        <div>

        </div>
    );
}
}

function mapStateToProps(state) {
    return {
        popular: state.popular,
        updatedList: state.displayList
    };
}


export default withRouter(connect(mapStateToProps, actions)(SearchPopular));

Answer 1

您正在以错误的方式声明更新。您要做的是，它将始终始终首先处理空数组，然后将其追加到其中。

case 'FETCH_POPULAR':
        return [...state, ...action.payload];

在您的减速器中尝试一下。

****对于您的主要问题，您正在尝试获取store.popular，但您在商店中并不受欢迎

const composeEnhancer = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose;

const configureStore = () => {
    const store = createStore(
        combineReducers({
            popular: Your reducer here
        }),
        composeEnhancer(applyMiddleware(thunk))
    );
    return store;
}

****新更新

我认为这是功能的问题，对此失去了参考。这就是我们this.getList.bind(this)在构造函数中使用的原因，因此，当我们调用this.getList该函数时，将获得对此的引用并可以使用它。因此，当您直接从任何其他函数调用它时，请使用this.getList.bind(this)

componentWillMount() {
        //console.log(this.props.match.params.format)
        this.props.fetchPopular(this.props.match.params.format, this.state.page);
        console.log(this.props.popular)
        console.log(this.getList.bind(this));
    }