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一、简介

        react中的状态只属于某个组件。而Redux是一个全局管理js状态的架构，让组件通信更加容易。

之前是状态在所有组件间传递，而redux通过store来实现这个功能。

Redux特性：

1.Single source Of truth，通过store唯一维护状态。

2.可预测性，state + action -> new state

3.纯函数更新store (纯函数 -> 输入决定输出)

举个例子: 待办事项表

function todos(state = [], action){switch(action.type){case 'ADD_TODO':return state.concat([{text: action.text, completed: false}]);case 'TOGGLE_TODO':return state.map((todo, idx) => {action.index === idx ? {text: todo.text, completed: !toto.completed}: todo})default:return state}}

二、核心概览

拿上图举个例子，前端ui产生了deposit和withdraw2个事件，store通过dispatcher分发对应的事件给reducer处理，reducer处理后更新state。前端ui根据state重新渲染。

1.store

Redux的状态机实现，store 通过state存储状态，通过dispatch传播事件，通过Reducer处理事件。

2.action

        action表示变更事件。一般包含event type 和 context。

3.Reducer

        reducer是状态事件处理。

举个例子: 待办事项表

function todoApp(state = initialState, action){switch (action.type){case ADD_TODO:return Object.assign({}, state, {todos:[...state.todos,{text: action.text,completed: false}]});default:return state;}
}

三、使用示例

用redux实现一个简单计数器，包括增加、减少功能。

import React from 'react';
import {createStore} from 'redux';
function run(){// store initial stateconst initialState = { count: 0};// reducerconst counter = (state = initialState, action) => {switch (action.type){case "PLUS_ONE":return {count: state.count + 1};case "MiNUS_ONE":return {count: state.count - 1};case "CUSTOM_COUNT":return {count: state.count + action.payload.count};default:return state;}  }// create storeconst store = createStore(counter);// Action creatorfunction plusOne(){return {type: "PLUS_ONE"}}function minusOne(){return {type: "MINUS_ONE"};}function customCount(count){return {type: "CUSTOM_COUNT", payload:{count}};}// 订阅redux 状态变更store.subscribe(() => console.log(store.getState()));store.dispatch(plusOne());store.dispatch(minusOne());store.dispatch(customCount(5));
}export default ()  => {<div><button onClick={run}>Run</button><p>* 请打开控制台查看运行结果</p></div>
}

bindActionCreators使用,工具类，可以减少显示dispatch操作

import React from 'react';
import {createStore, bindActionCreators} from 'redux';
function run(){// store initial stateconst initialState = { count: 0};// reducerconst counter = (state = initialState, action) => {switch (action.type){case "PLUS_ONE":return {count: state.count + 1};case "MiNUS_ONE":return {count: state.count - 1};case "CUSTOM_COUNT":return {count: state.count + action.payload.count};default:return state;}  }// create storeconst store = createStore(counter);// Action creatorfunction plusOne(){return {type: "PLUS_ONE"}}function minusOne(){return {type: "MINUS_ONE"};}function customCount(count){return {type: "CUSTOM_COUNT", payload:{count}};}plusOne = bindActionCreators(plusOne, store.dispatch);minusOne = bindActionCreators(minusOne, store.dispatch);customCount = bindActionCreators(customCount, store.dispatch);// 订阅redux 状态变更store.subscribe(() => console.log(store.getState()));plusOne();minusOne();customCount(5);
}export default ()  => {<div><button onClick={run}>Run</button><p>* 请打开控制台查看运行结果</p></div>
}

四、结合React使用

使用Connect功能，将redux的action和state作为props传递给组件。

计数器组件使用样例

import React from 'react';
import {createStore, bindActionCreators} from 'redux';
import {Provider, connect} fomr 'react-redux';// store initial state
const initialState = {count: 0};// reducer
const counter = (state = initialState, action) => {switch (action.type){case "PLUS_ONE":return {count: state.count + 1};case "MiNUS_ONE":return {count: state.count - 1};case "CUSTOM_COUNT":return {count: state.count + action.payload.count};default:return state;}  
}
// create store
const store = createStore(counter);
// Action creator
function plusOne(){return {type: "PLUS_ONE"}
}
function minusOne(){return {type: "MINUS_ONE"};
}export class Counter extends React.Component{render(){const {count, plusOne, minusOne} = this.props;return (<div className = "counter"><button onClick = {minusOne}>-</button><span>{count}</span><button onClick = {plusOne}>+</button></div>);}
}// 将store的state与组件props绑定
function mapStateToProps(state){return {count: state.count};
}// 将store的action与组件props绑定
function mapDispatchToProps(dispatch){return bindActionCreators({plusOne, minusOne}, dispatch)
}// 通过connect组件将store与counter组件关联
const ConnectedCounter = connect(mapStateToProps, mapDispatchToProps)(Counter) ;// 返回使用样例
export default class CounterSample extends React.Component{render(){return (// prodiver 基于react context实现，可以让里面的子组件都能获取到store<Provider store = {store}><ConnectedCounter/></Provider>);}
}