redux简明学习

2018-02-15 20:32:44来源:cnblogs.com作者:小火柴的蓝色理想人点击

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前面的话

  这几天被redux折腾的够呛,看了很多视频,也看了很多资料。很多时候,感觉好像顿悟了,但实际上只是理解了其中的一个小概念而已。真正去做项目的时候,还是会卡壳。可能是学CSS和Javascript时花的时间太久了,学redux的时候有点浮躁。还有就是redux内容实在是不少,全部都看都理解,好像没什么必要。不看吧,用的时候总是有点力不从心。于是,决定把这些资料按自己的理解写成博客,方便自己回忆思路,也希望能帮助到需要的人

核心概念

  redux专注于状态管理,把所有的状态都存在一个对象中。核心概念包括:store、state、action、reducer

【store】

  store是保存数据的地方,redux提供createStore函数来生成 Store。函数参数是后面要介绍的reducer

import { createStore } from 'redux'const store = createStore(reducer)

【state】

  state是store的某个时刻的快照,可以通过store.getState()取得当前时刻的state

const state = store.getState()

【action】

  action用来改变state。action是一个对象,其中的type属性是必须的,其他的属性一般用来设置改变state需要的数据

const action = {  type: 'ADD_ONE',  num: 1}

  store.dispatch()是发出action的唯一方法

const action = {  type: 'ADD_ONE',  num: 1}store.dispatch(action)

【reducer】

  reducer 是一个函数,它接受action和当前state作为参数,返回一个新的state

import { createStore } from 'redux'const store = createStore(reducer)
const reducer = (state = 10, action) => {  switch (action.type) {    case 'ADD_ONE':      return state + action.num;    default:       return state;  }};

  当store.dispatch发送过来一个新的action,store就会自动调用reducer,得到新的state

简单实例

  多余的概念不再介绍,下面用上面介绍的这四个核心概念实现一个简单的实例,将create-react-app中index.js文件内容更改如下,即可运行

//第一步,创建actionconst addOne = {  type: 'ADD',  num: 1}const addTwo = {  type: 'ADD',  num: 2}const square = {  type: 'SQUARE'}//第二步,创建reducerlet math = (state = 10, action) => {  switch (action.type) {    case ADD:      return state + action.num    case SQUARE:      return state * state    default:      return state  }}//第三步,创建storeimport { createStore } from 'redux'const store = createStore(math)//第四步,测试,通过dispatch发出action,并通过getState()取得当前state值console.log(store.getState()) //默认值为10store.dispatch(addOne) //发起'+1'的actionconsole.log(store.getState()) //当前值为10+1=11store.dispatch(square) //发起'乘方'的actionconsole.log(store.getState()) //当前值为11*11=121store.dispatch(addTwo) //发起'+2'的actionconsole.log(store.getState()) //当前值为121+2=123

  结果如下

目录结构

  下面对目录结构进行划分

  1、一般地,将action.type设置为常量,这样在书写错误时,会得到报错提示

// constants/ActionTypes.jsexport const ADD = 'ADD'export const SQUARE = 'SQUARE'

  2、可以将addOne对象和addTwo对象整合成add函数的形式

// action/math.jsimport { ADD, SQUARE } from '../constants/ActionTypes'export const add = num => ({ type: ADD, num })export const square = { type: SQUARE }

  3、根据action.type的分类来拆分reducer,最终通过combineReducers方法将拆分的reducer合并起来。上例中的action类型都是数字运算,无需拆分,只需进行如下变化

// reducer/math.jsimport { ADD, SQUARE } from '../constants/ActionTypes'const math = (state = 10, action) => {  switch (action.type) {    case ADD:      return state + action.num    case SQUARE:      return state * state    default:      return state  }}
export default math
// reducer/index.jsimport { combineReducers } from 'redux'import math from './math'const rootReducer = combineReducers({  math})export default rootReducer

  4、将store存储到store/index.js文件中

// store/index.jsimport { createStore } from 'redux'import rootReducer from '../reducer'export default createStore(rootReducer)

  5、最终,根路径下的index.js内容如下所示

import store from './store'import {add, square} from './action/math'console.log(store.getState()) //默认值为10store.dispatch(add(1)) //发起'+1'的actionconsole.log(store.getState()) //当前值为10+1=11store.dispatch(square) //发起'乘方'的actionconsole.log(store.getState()) //当前值为11*11=121store.dispatch(add(2)) //发起'+2'的actionconsole.log(store.getState()) //当前值为121+2=123

  最终目录路径如下所示

  最终结果如下所示

UI层

  前面的示例中,只是redux的状态改变,下面利用UI层来建立view和state的联系,将根目录下的index.js的内容更改如下

import store from './store'import React from 'react'import ReactDOM from 'react-dom'import { add, square } from './action/math'ReactDOM.render(  <div store={store}>    <p>{store.getState().math}</p>    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />  </div>,  document.getElementById('root'))

  虽然可以显示数字,但是点击按钮时,却不能重新渲染页面

【store.subscribe()】

  接下来介绍store.subscribe()方法了,该方法用来设置监听函数,一旦state发生变化,就自动执行这个函数。该方法的返回值是一个函数,调用这个函数可以解除监听

  下面将示例代码更改如下

import store from './store'import React from 'react'import ReactDOM from 'react-dom'import { add, square } from './action/math'const render = () => ReactDOM.render(  <div store={store}>    <p>{store.getState().math}</p>    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />  </div>,  document.getElementById('root'))render()store.subscribe(render)

  代码终于可以正常运行了

异步

  redux默认只处理同步,对于API请求这样的异步任务则无能为力

  接下来尝试使用axios的get方法来请求下面这个API

https://jsonplaceholder.typicode.com/posts/2

  获取的数据如下

{  "userId": 1,  "id": 2,  "title": "qui est esse",  "body": "est rerum tempore vitae/nsequi sint nihil reprehenderit dolor beatae ea dolores neque/nfugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis/nqui aperiam non debitis possimus qui neque nisi nulla"}

  然后,将其id值设置为state.math的值

  代码修改如下

// constants/ActionTypes.jsexport const ADD = 'ADD'export const SQUARE = 'SQUARE'export const SET = 'SET'// action/math.jsimport { ADD, SQUARE, SET } from '../constants/ActionTypes'export const add = num => ({ type: ADD, num })export const square = { type: SQUARE }export const setNum = num => ({type: SET,num})// reduce/math.jsimport { ADD, SQUARE,SET } from '../constants/ActionTypes'const math = (state = 10, action) => {  switch (action.type) {    case ADD:      return state + action.num    case SQUARE:      return state * state    case SET:      return action.num    default:      return state  }}export default math// index.jsimport store from './store'import React from 'react'import ReactDOM from 'react-dom'import { add, square, setNum } from './action/math'import axios from 'axios'let uri = 'https://jsonplaceholder.typicode.com/posts/2'const render = () => ReactDOM.render(  <div store={store}>    <p>{store.getState().math}</p>    <input type="button" onClick={() => {axios.get(uri).then(res => {store.dispatch(store.dispatch(setNum(res.data.id)))})}} value="设置Num" />    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />  </div>,  document.getElementById('root'))render()store.subscribe(render)

  效果如下

  但是,虽然API是异步操作,但store.dispatch并不是异步,而axios通过get方法请求回来数据后,store.dispatch在axios中的then方法中同步取得数据

【redux-thunk】

  如果要使用真正的异步操作,即把axios方法封装到store.dispatch中,需要使用redux-thunk中间件

  首先,使用npm进行安装

npm install --save redux-thunk

  然后,使用applyMiddleware来使用thunk中间件

import { createStore, applyMiddleware } from 'redux'import thunk from 'redux-thunk'import rootReducer from '../reducer'export default createStore(rootReducer,applyMiddleware(thunk))

  接着来定义setNum这个action creator,然后在index.js文件的DOM加载完成后就发出setNum

  [注意]如果action是一个对象,则它就是一个action,如果action是一个函数,则它是一个action creator,即action制造器

  修改的代码如下

// action/math.jsimport { ADD, SQUARE, SET } from '../constants/ActionTypes'import axios from 'axios'const uri = 'https://jsonplaceholder.typicode.com/posts/2'export const add = num => ({ type: ADD, num })export const square = { type: SQUARE }export const setNum = () => (dispatch, getState) => {  return axios.get(uri).then(res => {    dispatch({      type: SET,      num: res.data.id    })  })}// index.jsimport store from './store'import React from 'react'import ReactDOM from 'react-dom'import { add, square, setNum } from './action/math'const render = () => ReactDOM.render(  <div store={store}>    <p>{store.getState().math}</p>    <input type="button" onClick={() => store.dispatch(setNum())} value="设置Num" />    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />  </div>,  document.getElementById('root'))render()store.subscribe(render)

  效果如下

【提示信息】

  如果做的更完备一点,应该把异步请求时的提示信息也加上。增加一个fetch的action,用于控制fetch过程的提示信息及显示隐藏情况

  代码更改如下

// action/fetch.jsimport { SET_FETCH_MESSAGE, HIDE_FETCH_MESSAGE } from '../constants/ActionTypes'export const startFetch = { type: SET_FETCH_MESSAGE,message: '开始发送异步请求' }export const successFetch = { type: SET_FETCH_MESSAGE, message: '成功接收数据' }export const failFetch = { type: SET_FETCH_MESSAGE, message: '接收数据失败' }export const hideFetchMessage = { type: HIDE_FETCH_MESSAGE }
// action/math.jsimport { ADD, SQUARE, SET } from '../constants/ActionTypes'import { startFetch, successFetch, failFetch, hideFetchMessage } from './fetch'import axios from 'axios'const uri = 'https://jsonplaceholder.typicode.com/posts/2'export const add = num => ({ type: ADD, num })export const square = { type: SQUARE }export const setNum = () => (dispatch, getState) => {  dispatch(startFetch)  setTimeout(() => {    dispatch(hideFetchMessage)  }, 500)  return axios    .get(uri)    .then(res => {      setTimeout(() => {        dispatch(successFetch)        setTimeout(() => {          dispatch(hideFetchMessage)        }, 500)        dispatch({ type: SET, num: res.data.id })      }, 1000)    })    .catch(err => {      dispatch(failFetch)      setTimeout(() => {        dispatch(hideFetchMessage)      }, 500)    })}
// constants/ActionTypes.jsexport const ADD = 'ADD'export const SQUARE = 'SQUARE'export const SET = 'SET'export const SET_FETCH_MESSAGE = 'SET_FETCH_MESSAGE'export const HIDE_FETCH_MESSAGE = 'HIDE_FETCH_MESSAGE'
// reduce/fetch.jsimport { SET_FETCH_MESSAGE,HIDE_FETCH_MESSAGE } from '../constants/ActionTypes'const initState = {  message:'',  isShow:false}const fetch = (state = initState, action) => {  switch (action.type) {    case SET_FETCH_MESSAGE:      return {isShow: true, message: action.message}    case HIDE_FETCH_MESSAGE:      return { isShow: false, message: '' }    default:      return state  }}export default fetch
// index.jsimport store from './store'import React from 'react'import ReactDOM from 'react-dom'import { add, square, setNum } from './action/math'const render = () => ReactDOM.render(  <div store={store}>    <p>{store.getState().math}</p>    <input type="button" onClick={() => store.dispatch(setNum())} value="设置Num" />    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />    {store.getState().fetch.isShow && <p>{store.getState().fetch.message}</p>}  </div>,  document.getElementById('root'))render()store.subscribe(render)

  效果如下

  

展示和容器

  下面来介绍react-redux。前面的代码中,我们是通过store.subscribe()方法监控state状态的变化来更新UI层的。而使用react-redux,可以让组件动态订阅状态树。状态树一旦被修改,组件能自动刷新显示最新数据

  react-redux将所有组件分成两大类:展示组件和容器组件。展示组件只负责UI呈现,所有数据由参数props提供;容器组件则负责管理数据和业务逻辑,带有内部状态,可使用redux的API。要使用react-redux,就要遵守它的组件拆分规范

【provider】

  react-redux提供Provider组件,可以让容器组件默认可以拿到state,而不用当容器组件层级很深时,一级级将state传下去

  将index.js文件更改如下

// index.jsimport React from 'react'import ReactDOM from 'react-dom'import store from './store'import MathContainer from './container/MathContainer'import { Provider } from 'react-redux'ReactDOM.render(  <Provider store={store}>    <MathContainer />  </Provider>,  document.getElementById('root'))

  按照组件拆分规范,将原来index.js中相关代码,分拆到container/MathContainer和component/Math这两个组件中

【connect】

  react-redux提供connect方法,用于从展示组件生成容器组件。connect的意思就是将这两种组件连接起来

import { connect } from 'react-redux'const MathContainer = connect()(Math);

  Math是展示组件,MathContainer就是由React-redux通过connect方法自动生成的容器组件

  为了定义业务逻辑,需要给出下面两方面的信息

  1、输入逻辑:外部的数据(即state对象)如何转换为展示组件的参数

  2、输出逻辑:用户发出的动作如何变为Action对象,从展示组件传出去

  因此,connect方法的完整API如下

import {connect} from 'react-redux'const MathContainer= connect(    mapStateToProps,    mapDispatchToProps)(Math)

  上面代码中,connect方法接受两个参数:mapStateToProps和mapDispatchToProps。它们定义了展示组件的业务逻辑。前者负责输入逻辑,即将state映射到UI组件的参数(props),后者负责输出逻辑,即将用户对展示组件的操作映射成Action

【mapStateToProps()】

  mapStateToProps建立一个从外部的state对象到展示组件的props对象的映射关系。作为参数,mapStateToProps执行后应该返回一个对象,里面的每一个键值对就是一个映射。

const mapStateToProps = (state) => {  return {    num: getNum(state)                    }  }

  mapStateToProps的第一个参数总是state对象,还可以使用第二个参数,代表容器组件的props对象。使用ownProps作为参数后,如果容器组件的参数发生变化,也会引发展示组件重新渲染

const mapStateToProps = (state,ownProps) => {  return {    num: getNum(state)                    }  }

  mapStateToProps会订阅Store,每当state更新的时候,就会自动执行,重新计算展示组件的参数,从而触发展示组件的重新渲染。connect方法可以省略mapStateToProps参数,那样,展示组件就不会订阅Store,就是说Store的更新不会引起展示组件的更新

【mapDispatchToProps】

  mapDispatchToProps是connect函数的第二个参数,用来建立展示组件的参数到store.dispatch方法的映射。也就是说,它定义了用户的哪些操作应该当作action,传给Store。它可以是一个函数,也可以是一个对象

  如果mapDispatchToProps是一个函数,会得到dispatch和ownProps(容器组件的props对象)两个参数

const mapDispatchToProps = (dispatch,ownProps) => {  return {    onSetNumClick: () => dispatch(setNum())  }}

  mapDispatchToProps作为函数,应该返回一个对象,该对象的每个键值对都是一个映射,定义了展示组件的参数怎样发出action

  如果mapDispatchToProps是一个对象,它的每个键名也是对应展示组件的同名参数,键值应该是一个函数,会被当作action creator,返回的action会由redux自动发出

  因此,上面的写法简写如下所示

const mapDispatchToProps = {  onsetNumClick: () => setNum()}

最终结构

  由于store目录中,只能一个index.js文件,且不会有内容扩展,将其更改为根目录下的store.js文件

  将其他的目录都变成复数形式,最终的目录结构如下所示

  效果如下

  详细代码如下所示,且可访问github线上地址

【components】

// components/Math.jsimport React from 'react'const Math = ({  num,  isShow,  fetchMessage,  onSetNumClick,  onAddOneClick,  onAddTwoClick,  onSqureClick}) => (  <section>    <p>{num}</p>    <input type="button" onClick={onSetNumClick} value="设置Num" />    <input type="button" onClick={onAddOneClick} value="+1" />    <input type="button" onClick={onAddTwoClick} value="+2" />    <input type="button" onClick={onSqureClick} value="乘方" />    {isShow && <p>{fetchMessage}</p>}  </section>)export default Math

【containers】

// containers/MathContainer.jsimport { connect } from 'react-redux'import Math from '../components/Math'import { getNum } from '../selectors/math'import { getFetchMessage, getFetchIsShow } from '../selectors/fetch'import { setNum, add, square } from '../actions/math'const mapStateToProps = state => {  return {    num: getNum(state),    fetchMessage: getFetchMessage(state),    isShow: getFetchIsShow(state)  }}const mapDispatchToProps = {  onSetNumClick: () => setNum(),  onAddOneClick: () => add(1),  onAddTwoClick: () => add(2),  onSqureClick: () => square}const MathContainer = connect(mapStateToProps, mapDispatchToProps)(Math)export default MathContainer

【actions】

// actions/fetch.jsimport { SET_FETCH_MESSAGE, HIDE_FETCH_MESSAGE } from '../constants/ActionTypes'export const startFetch = { type: SET_FETCH_MESSAGE,message: '开始发送异步请求' }export const successFetch = { type: SET_FETCH_MESSAGE, message: '成功接收数据' }export const failFetch = { type: SET_FETCH_MESSAGE, message: '接收数据失败' }export const hideFetchMessage = { type: HIDE_FETCH_MESSAGE }
// actions/math.jsimport { ADD, SQUARE, SET } from '../constants/ActionTypes'import { startFetch, successFetch, failFetch, hideFetchMessage } from './fetch'import axios from 'axios'const uri = 'https://jsonplaceholder.typicode.com/posts/2'export const add = num => ({ type: ADD, num })export const square = { type: SQUARE }export const setNum = () => (dispatch, getState) => {  dispatch(startFetch)  setTimeout(() => {dispatch(hideFetchMessage)}, 300)  return axios    .get(uri)    .then(res => {      dispatch(successFetch)      setTimeout(() => {dispatch(hideFetchMessage)}, 300)      dispatch({ type: SET, num: res.data.id })    })    .catch(err => {      dispatch(failFetch)      setTimeout(() => {dispatch(hideFetchMessage)}, 300)    })}

【constants】

// constants/ActionTypes.jsexport const ADD = 'ADD'export const SQUARE = 'SQUARE'export const SET = 'SET'export const SET_FETCH_MESSAGE = 'SET_FETCH_MESSAGE'export const HIDE_FETCH_MESSAGE = 'HIDE_FETCH_MESSAGE'

【reducers】

// reducers/fetch.jsimport { SET_FETCH_MESSAGE,HIDE_FETCH_MESSAGE } from '../constants/ActionTypes'const initState = {  message:'',  isShow:false}const fetch = (state = initState, action) => {  switch (action.type) {    case SET_FETCH_MESSAGE:      return {isShow: true, message: action.message}    case HIDE_FETCH_MESSAGE:      return { isShow: false, message: '' }    default:      return state  }}export default fetch
// reducers/index.jsimport { combineReducers } from 'redux'import math from './math'import fetch from './fetch'const rootReducer = combineReducers({  math,  fetch})export default rootReducer
// reduces/math.jsimport { ADD, SQUARE,SET } from '../constants/ActionTypes'const math = (state = 10, action) => {  switch (action.type) {    case ADD:      return state + action.num    case SQUARE:      return state * state    case SET:      return action.num    default:      return state  }}export default math

【selectors】

// selectors/fetch.jsexport const getFetchMessage = state => state.fetch.messageexport const getFetchIsShow = state => state.fetch.isShow
// selectors/math.jsexport const getNum = state => state.math

【根目录】

// index.jsimport React from 'react'import ReactDOM from 'react-dom'import store from './store'import MathContainer from './containers/MathContainer'import { Provider } from 'react-redux'ReactDOM.render(  <Provider store={store}>    <MathContainer />  </Provider>,  document.getElementById('root'))
// store.jsimport { createStore, applyMiddleware } from 'redux'import thunk from 'redux-thunk'import rootReducer from './reducers'export default createStore(rootReducer,applyMiddleware(thunk))
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