【前端知识】React 基础巩固(三十四)——组件中的异步操作及优化

React 基础巩固(三十四)------组件中的异步操作及优化

一、待优化的异步请求流程

• 通过组件的生命周期来完成网络请求，网络请求的异步代码直接放在组件中

import React, { PureComponent } from "react";
import { connect } from "react-redux";
import {
  changeBannerAction,
  changeRecommendAction,
} from "../store/actionCreators";
import axios from "axios";

export class category extends PureComponent {
  componentDidMount() {
    axios.get("http://123.207.32.32:8000/home/multidata").then((res) => {
      console.log(res.data);
      const banners = res.data.data.banner.list;
      const recommends = res.data.data.recommend.list;
      console.log(banners, recommends);
      this.props.changeBanners(banners);
      this.props.changeRecommends(recommends);
    });
  }

  render() {
    return <div>category</div>;
  }
}

const mapDispatchToProps = (dispatch) => ({
  changeBanners(banners) {
    dispatch(changeBannerAction(banners));
  },
  changeRecommends(recommends) {
    dispatch(changeRecommendAction(recommends));
  },
});

export default connect(null, mapDispatchToProps)(category);

二、利用Redux优化异步网络请求

• 通过redux来管理异步网络请求
  

• 在store中引入中间件redux-thunk

  import { createStore, applyMiddleware } from "redux";
  import reducer from "./reducer";
  import thunk from "redux-thunk";
  
  // 正常情况下，store.dispatch 只能派发对象
  // 想要派发函数，需要增强，使用 "redux-thunk"
  
  const store = createStore(reducer, applyMiddleware(thunk));
  
  export default store;

• 构建fetchHomeMultidataAction，将原本在组件中的异步请求代码放入到actionCreators.js中

  import * as actionTypes from "./constants";
  import axios from "axios";
  
  export const addNumberAction = (num) => ({
    type: actionTypes.ADD_NUMBER,
    num,
  });
  
  export const subNumberAction = (num) => ({
    type: actionTypes.SUB_NUMBER,
    num,
  });
  
  export const changeBannerAction = (banners) => ({
    type: actionTypes.CHANGE_BANNERS,
    banners,
  });
  
  export const changeRecommendAction = (recommends) => ({
    type: actionTypes.CHANGE_RECOMMENDS,
    recommends,
  });
  
  export const fetchHomeMultidataAction = () => {
    return (dispatch, getState) => {
      // 异步操作
      axios.get("http://123.207.32.32:8000/home/multidata").then((res) => {
        const banners = res.data.data.banner.list;
        const recommends = res.data.data.recommend.list;
        dispatch(changeBannerAction(banners))
        dispatch(changeRecommendAction(recommends))
      });
    }
  };

• 改写原来的category.jsx，派发异步请求的dispatch

  import React, { PureComponent } from "react";
  import { connect } from "react-redux";
  import { fetchHomeMultidataAction } from "../store/actionCreators";
  // import axios from "axios";
  
  export class category extends PureComponent {
    componentDidMount() {
      // axios.get("http://123.207.32.32:8000/home/multidata").then((res) => {
      //   console.log(res.data);
      //   const banners = res.data.data.banner.list;
      //   const recommends = res.data.data.recommend.list;
      //   console.log(banners, recommends);
      //   this.props.changeBanners(banners);
      //   this.props.changeRecommends(recommends);
      // });
  
      this.props.fetchHomeMultidata();
    }
  
    render() {
      const { banners, recommends } = this.props;
      return (
        <div>
          category
          <div className="banner">
            <h2>轮播图：</h2>
            <ul>
              {banners.map((item, index) => {
                return <li key={index}>{item.title}</li>;
              })}
            </ul>
          </div>
          <div className="recommend">
            <h2>推荐数据：</h2>
            <ul>
              {recommends.map((item, index) => {
                return <li key={index}>{item.title}</li>;
              })}
            </ul>
          </div>
        </div>
      );
    }
  }
  
  const mapStateToProps = (state) => ({
    counter: state.counter,
    banners: state.banners,
    recommends: state.recommends,
  });
  
  const mapDispatchToProps = (dispatch) => ({
    //   changeBanners(banners) {
    //     dispatch(changeBannerAction(banners));
    //   },
    //   changeRecommends(recommends) {
    //     dispatch(changeRecommendAction(recommends));
    //   },
    fetchHomeMultidata(recommends) {
      dispatch(fetchHomeMultidataAction(recommends));
    },
  });
  
  export default connect(mapStateToProps, mapDispatchToProps)(category);

• 查看运行结果