why redux?

• 随着 JavaScript 单页应用开发日趋复杂,管理不断变化的 state 非常困难
• Redux的出现就是为了解决state里的数据问题
• 在React中，数据在组件中是单向流动的
• 数据从一个方向父组件流向子组件(通过props)，由于这个特征，两个非父子关系的组件（或者称作兄弟组件）之间的通信比较麻烦

what is redux?

工作流

设计思想

• Redux是将整个应用状态存储到到一个地方，称为store
• store里面保存一棵状态树(state tree)
• 组件可以派发(dispatch)行为(action)给store,而不是直接通知其它组件
• 其它组件可以通过订阅store中的状态(state)来刷新自己的视图.

三大原则

• 整个应用的 state 被储存在一棵 object tree 中，并且这个 object tree 只存在于唯一一个 store 中 State 是只读的，惟一改变 state 的方法就是触发 action，
• action是一个用于描述已发生事件的普通对象 使用纯函数来执行修改，为了描述action如何改变state tree ，你需要编写 reducers
• 单一数据源的设计让React的组件之间的通信更加方便，同时也便于状态的统一管理

how redux?

1.安装

npm i redux -S
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2.简单例子

1.引入

import {createStore} from 'redux';
//createStore 用来创建状态仓库
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2.创建state

let initState = {title: 'star'
}
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3.创建reducer

const CHANGETITLE = 'CHANGETITLE'; //action-todos
function reducer(state= initState, action){switch(action.type){case CHANGETITLE: return state.title = action.title;}}
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4.创建仓库

let store = createStore(reducer);
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5.触发dispatch中传入action

store.dispatch({type: CHANGETITLE, title: 'xingxing'})
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完整代码

import {createStore} from 'redux';
const CHANGETITLE = 'CHANGETITLE';
function reducer(state= initState, action){switch(action.type){case CHANGETITLE: state.title = action.title;}console.log(state);
}
let store = createStore(reducer);
store.subscribe(()=>{                    //订阅事件，在dispatch时触发console.log('render');
})
store.dispatch({type: CHANGETITLE, title: 'xingxing'})
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复杂些例子

在真实开发中需要开辟一个文件空间来管理仓库

• 文件结构化
• 多reducer，合并reducer

1.actions

action-type.js

//action-type衡量,通过引入使用，减少拼写错误引发的问题
export const INCREMENT = 'INCREMENT'
export const DECREMNET = 'DECREMNET'
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actions/count.js

import * as types from "../action-types"
//用于生成action
let counter = {add(n){return {type: types.INCREMENT, count: n}}
}
export default counter
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2.reducers

reducers/count.js

import {INCREMENT,DECREMENT} from '../actions/action-type'
let initState = {count: 0
}
function reducer(state = initState,action){switch(action.type){case INCREMENT:state.count = state.count + action.number;break;case DECREMENT:state.count = state.count - action.number;break;}return state
}
export default reducer
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合并reducer

reducers/index.js

import todos from './todo';
import count from './count';
import {combineReducers} from 'redux'
let reducers = combineReducers({todos,count
})
export default reducers;
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store/index.js 初始化仓库

import {INCEMENT,DECREMENT} from './actions/action-type';
import {createStore} from 'redux';
import reducers from './reducers'export default createStore(reducers);
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how is redux work?

• redux的数据源是创建reducer时，传进去的initState。
• 为了避免state被随意篡改，redux通过dispatch reducer来更改数据。
• redux可以通过subscribe订阅状态修改事件

//简单实现
function createStore(reducer){let state;let listeners = [];function subscribe(listener){listeners.push(listener);return ()=> listeners = listeners.filter(fn=>fn!==listener);}function dispatch(action){listeners.forEach(listener=>listener());reducer(state, action)}dispatch({})function getState(){return state;}return {subscribe, dispatch, getState}
}
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合并reducer

function combineReducers(reducers){return (state={},action)=>{let newState = {};for(let key in reducers){let s = reducers[key](state[key],action);newState[key] = s;}return newState;}
}
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完整代码

function createStore(reducer){let state;let listeners = [];function subscribe(listener){listeners.push(listener);return ()=>{listeners = listeners.filter(l=> l!==listener)}}dispatch({})function dispatch(action){state = reducer(state,action);listeners.forEach(l=>l());}function getState(){return state;}return {subscribe,dispatch,getState};
}function combineReducers(reducers){return (state={},action)=>{let newState = {};for(let key in reducers){let s = reducers[key](state[key],action);  newState[key] = s;}return newState;}
}export {createStore,combineReducers}
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最近在研究redux，欢迎指出问题。后续更新react-redux全家桶系列研究