React 基础巩固(三十二)——Redux的三大原则

一、Redux的三大原则

1. 单一数据源

   • 整个应用程序的state被存储在一颗object tree 中，并且这个object tree 只存储在一个store中；
   • Redux并没有强制让我们不能创建多个Store，但是那样做不利于数据维护；
   • 单一的数据源可以让整个应用程序的state变得方便维护、追踪、修改；

2. State是只读的

   • 唯一修改State的方法一定是触发action，不要试图在其他地方通过任何的方式来修改State；

   • 这样就确保了View或网络请求都不能直接修改state，它们只能通过action来描述自己想要如何修改state；

   • 这样可以保证所有的修改都被集中化处理，并且按照严格的顺序来执行，所以不需要担心reace condition（竞态）的问题；

3. 使用纯函数来执行修改

   • 通过reducer将旧state和actions联系在一起，并且返回一个新的state；
   • 随着应用程序的复杂度增加，我们可以将reducer拆分成多个小的reducers，分别操作不同state tree 的一部分；
   • 但是所有的reducer都应该是纯函数，不能产生任何的副作用；

二、Redux的使用流程

三、Redux的基本使用（计数器小案例）

1. 构建react项目

   # 创建新的react项目
   create-react-app redux-learn
   # 创建成功后cd进入文件夹，随后安装redux
   npm install redux
   

2. 删除暂时无关文件，构建store相关文件，并引用store至所需页面中

   • 目录

• store/constants.js

  export const ADD_NUMBER = "add_number";
  export const SUB_NUMBER = "sub_number";
  

• store/reducer.js

  import * as actionTypes from "./constants";const initialState = {counter: 111,
  };function reducer(state = initialState, action) {switch (action.type) {case actionTypes.ADD_NUMBER:return { ...state, counter: state.counter + action.num };case actionTypes.SUB_NUMBER:return { ...state, counter: state.counter - action.num };default:return state;}
  }export default reducer;

• store/actionCreators.js

  import * as actionTypes from "./constants";export const addNumberAction = (num) => ({type: actionTypes.ADD_NUMBER,num,
  });export const subNumberAction = (num) => ({type: actionTypes.SUB_NUMBER,num,
  });

• store/index.js

  import { createStore } from "redux";
  import reducer from "./reducer";const store = createStore(reducer);export default store;

• pages/home.jsx

  import React, { PureComponent } from "react";
  import store from "../store";
  import { addNumberAction } from "../store/actionCreators";
  export class home extends PureComponent {constructor() {super();this.state = {counter: store.getState().counter,};}componentDidMount() {store.subscribe(() => {const state = store.getState();this.setState({counter: state.counter,});});}addNumber(num) {store.dispatch(addNumberAction(num));}render() {const { counter } = this.state;return (<div>home counter:{counter}<div><button onClick={(e) => this.addNumber(1)}>+1</button><button onClick={(e) => this.addNumber(5)}>+5</button><button onClick={(e) => this.addNumber(8)}>+8</button></div></div>);}
  }export default home;

• pages/profile.jsx

  import React, { PureComponent } from "react";
  import store from "../store";
  import { subNumberAction } from "../store/actionCreators";
  export class profile extends PureComponent {constructor() {super();this.state = {counter: store.getState().counter,};}componentDidMount() {store.subscribe(() => {const state = store.getState();this.setState({counter: state.counter,});});}subNumber(num) {store.dispatch(subNumberAction(num));}render() {const { counter } = this.state;return (<div>profile counter:{counter}<div><button onClick={(e) => this.subNumber(1)}>-1</button><button onClick={(e) => this.subNumber(5)}>-5</button><button onClick={(e) => this.subNumber(8)}>-8</button></div></div>);}
  }export default profile;

• App.jsx

  import React, { PureComponent } from "react";
  import Home from "./pages/home";
  import Profile from "./pages/profile";
  import "./style.css";
  import store from "./store";export class App extends PureComponent {constructor() {super();this.state = {counter: store.getState().counter,};}componentDidMount() {store.subscribe(() => {const state = store.getState();this.setState({counter: state.counter,});});}render() {const { counter } = this.state;return (<div><h2>App Counter: {counter}</h2><div className="pages"><Home /><Profile /></div></div>);}
  }export default App;

3. 运行结果
   

至此，代码仍较为复杂，代码将在React 基础巩固(三十三)中得到优化