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1、回顾纯函数

2、redux

2.1 redux的基本使用

• pm install redux --save
• 
• store

const { createStore } = require("redux");// 1.state数据
const initialState = {name: "kiki",age: "18",
};// 2.reducer纯函数
function reducer() {return initialState;
}// 3.创建store
const store = createStore(reducer);module.exports = store;

2.2 通过action修改store的数值

const { createStore } = require("redux");
const { ADD_NUMBER, CHANGE_NAME } = require("./constants");// 1.state数据
const initialState = {name: "kiki",num: 18,
};// 2.reducer纯函数// 两个参数
// 参数1：store目前保存的state 设置默认参数
// 参数2：本次需要更新的action
// 返回值 他的返回值作为之后存储在store的数值 因为第一次调用没有数值 所以设置默认值
function reducer(state = initialState, action) {console.log(state, action); // { name: 'kiki', num: '18' } { type: '@@redux/INIT0.n.r.y.w.j' }switch (action.type) {case ADD_NUMBER:// 这里需要创建新的对象的返回 否则页面发现state没有发生变化不会更新界面return { ...state, num: state.num + action.num };case CHANGE_NAME:return { ...state, name: action.name };default:return state;}
}// 3.创建store
const store = createStore(reducer);module.exports = store;

2.3 订阅state的变化

2.4 目录结构

2.5 Redux的使用过程

2.6 redux的三大原则

2.7 Redux官方图

3、redux在React中的使用

4、react-redux使用

yarn add react-redux

4.1 react-redux的基本使用

import React, { PureComponent } from "react";
import { connect } from "react-redux";
// import store from "../store"
import { addNumberAction, subNumberAction } from "../store/actionCreators";export class About extends PureComponent {calcNumber(num, isAdd) {if (isAdd) {console.log("加", num);this.props.addNumber(num);} else {console.log("减", num);this.props.subNumber(num);}}render() {const { counter, banners, recommends } = this.props;return (<div><h2>About Page: {counter}</h2><div><button onClick={(e) => this.calcNumber(6, true)}>+6</button><button onClick={(e) => this.calcNumber(88, true)}>+88</button><button onClick={(e) => this.calcNumber(6, false)}>-6</button><button onClick={(e) => this.calcNumber(88, false)}>-88</button></div></div>);}
}// connect()返回值是一个高阶组件
// function mapStateToProps(state) {
//   return {
//     counter: state.counter
//   }
// }// function fn2(dispatch) {
//   return {
//     addNumber(num) {
//       dispatch(addNumberAction(num))
//     },
//     subNumber(num) {
//       dispatch(subNumberAction(num))
//     }
//   }
// }const mapStateToProps = (state) => ({counter: state.counter,banners: state.banners,recommends: state.recommends,
});const mapDispatchToProps = (dispatch) => ({addNumber(num) {dispatch(addNumberAction(num));},subNumber(num) {dispatch(subNumberAction(num));},
});// connect是高阶组件
export default connect(mapStateToProps, mapDispatchToProps)(About);

4.2 异步请求 redux-thunk

yarn add redux-thunk

4.3 对redux代码结构进行优化 和 redux-devtools

每个页面可能都会有自己的store为了方便维护，将store按照页面划分

import { createStore, applyMiddleware, compose, combineReducers } from "redux";
import thunk from "redux-thunk";import counterReducer from "./counter";
import homeReducer from "./home";
import userReducer from "./user";// 正常情况下 store.dispatch(object)
// 想要派发函数 store.dispatch(function)// 将两个reducer合并在一起
const reducer = combineReducers({counter: counterReducer,home: homeReducer,user: userReducer,
});// combineReducers实现原理(了解)
// function reducer(state = {}, action) {
//   // 返回一个对象, store的state
//   return {
//     counter: counterReducer(state.counter, action),
//     home: homeReducer(state.home, action),
//     user: userReducer(state.user, action)
//   }
// }// redux-devtools
// trace的功能是可以追踪源码
const composeEnhancers =window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__({ trace: true }) || compose;// thunk 是用来发送异步请求的增强写法
const store = createStore(reducer, composeEnhancers(applyMiddleware(thunk)));export default store;

5、ReduxToolkit

5.1 基本使用

npm install @reduxjs/toolkit react-redux

• 需要在根组件传递store的值
  
  
  

import React, { PureComponent } from "react";
import { connect } from "react-redux";
import { changeNumber } from "../store/features/counter";export class About extends PureComponent {changeNum(num) {this.props.changeNumber(num);}render() {const { counter } = this.props;return (<div>{counter}<button onClick={(e) => this.changeNum(5)}>+5</button></div>);}
}const mapStateToProps = (state) => ({counter: state.counter.counter,
});const mapDispatchToProps = (dispatch) => ({changeNumber(num) {dispatch(changeNumber(num));},
});export default connect(mapStateToProps, mapDispatchToProps)(About);

5.2 异步操作 写法1

import { createAsyncThunk } from "@reduxjs/toolkit";
import { createSlice } from "@reduxjs/toolkit";
import axios from "axios";// toolkit已经集成了thunk所以可以直接使用
// 第一个参数是name可以根据自己的喜好取
// 可以把这个函数看成是promise 它跟promise十分相似
export const fetchHomeMultidataAction = createAsyncThunk("fetch/homemultidata",// dispatch传递的参数是第一个 extraInfoasync (extraInfo, { dispatch, getState }) => {console.log(extraInfo);const res = await axios.get("http://123.207.32.32:8000/home/multidata");// 不能直接返回res 没办法直接对其进行序列化return res.data;}
);const homeSlice = createSlice({name: "home",initialState: {banner: [],},reducers: {changeBanner(state, { payload }) {state.banner = payload;},},// 这里是对异步操作进行操作的方法extraReducers: {[fetchHomeMultidataAction.pending](state, action) {console.log(action);},[fetchHomeMultidataAction.fulfilled](state, { payload, meta }) {// 异步操作返回的参数state.banner = payload.data.banner.list;// 在dispatch时传递的参数console.log(meta.arg);},[fetchHomeMultidataAction.rejected](state, action) {console.log("fetchHomeMultidataAction rejected");},},
});export const { changeBanner } = homeSlice.actions;
export default homeSlice.reducer;

5.3 异步操作 写法2

import { createAsyncThunk } from "@reduxjs/toolkit";
import { createSlice } from "@reduxjs/toolkit";
import axios from "axios";// toolkit已经集成了thunk所以可以直接使用
// 第一个参数是name可以根据自己的喜好取
// 可以把这个函数看成是promise 它跟promise十分相似
export const fetchHomeMultidataAction = createAsyncThunk("fetch/homemultidata",// dispatch传递的参数是第一个 extraInfoasync (extraInfo, { dispatch, getState }) => {console.log(extraInfo);const res = await axios.get("http://123.207.32.32:8000/home/multidata");// 不能直接返回res 没办法直接对其进行序列化return res.data;}
);const homeSlice = createSlice({name: "home",initialState: {banner: [],},reducers: {changeBanner(state, { payload }) {state.banner = payload;},},// 这里是对异步操作进行操作的方法// extraReducers: {//   [fetchHomeMultidataAction.pending](state, action) {//     console.log(action);//   },//   [fetchHomeMultidataAction.fulfilled](state, { payload, meta }) {//     // 异步操作返回的参数//     state.banner = payload.data.banner.list;//     // 在dispatch时传递的参数//     console.log(meta.arg);//   },//   [fetchHomeMultidataAction.rejected](state, action) {//     console.log("fetchHomeMultidataAction rejected");//   },// },extraReducers: (builder) => {builder.addCase(fetchHomeMultidataAction.pending, (state, action) => {console.log("fetchHomeMultidataAction pending");}).addCase(fetchHomeMultidataAction.fulfilled, (state, { payload }) => {state.banners = payload.data.banner.list;state.recommends = payload.data.recommend.list;});},
});export const { changeBanner } = homeSlice.actions;
export default homeSlice.reducer;

6、手写connext

// connect的参数:
// 参数一: 函数
// 参数二: 函数
// 返回值: 函数 => 高阶组件import { PureComponent } from "react";
import { StoreContext } from "./StoreContext";
// import store from "../store"//  实际上就是一个高阶函数里面嵌套一个高阶组件
export function connect(mapStateToProps, mapDispatchToProps, store) {// 高阶组件: 函数return function (WrapperComponent) {class NewComponent extends PureComponent {//  接收的第二个参数就是contextconstructor(props, context) {super(props);this.state = mapStateToProps(context.getState());}componentDidMount() {// 因为页面发生改变是connect自己内部实现的 我们自己手写的话 要手动调用this.unsubscribe = this.context.subscribe(() => {// 不能直接通过强制刷新 不然性能很低// this.forceUpdate()// 执行ToProps的方法 自己判断是否state发生了变化this.setState(mapStateToProps(this.context.getState()));});}componentWillUnmount() {this.unsubscribe();}render() {// 传递进来的两个方法进行调用 再把他们的数值传递给组件 实现了高阶组件的增强const stateObj = mapStateToProps(this.context.getState());const dispatchObj = mapDispatchToProps(this.context.dispatch);return (<WrapperComponent {...this.props} {...stateObj} {...dispatchObj} />);}}// 为了避免每次store都是需要传入进来 所以创建了一个context 在注册应用的时候就将他导入NewComponent.contextType = StoreContext;return NewComponent;};
}

7、合并中间件

8、React中的state如何管理