redux 简明学习

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action
const addOne = {
  type: 'ADD',
  num: 1
}
const addTwo = {
  type: 'ADD',
  num: 2
}
const square = {
  type: 'SQUARE'
}

//第二步，创建reducer
let 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store
import { 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10

store.dispatch(addOne) //发起'+1'的action
console.log(store.getState()) //当前值为10+1=11

store.dispatch(square) //发起'乘方'的action
console.log(store.getState()) //当前值为11*11=121

store.dispatch(addTwo) //发起'+2'的action
console.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.js
export 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.js
import { 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.js

// reducer/math.js
import { 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.js

// reducer/index.js
import { 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.js
import { 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10

store.dispatch(add(1)) //发起'+1'的action
console.log(store.getState()) //当前值为10+1=11

store.dispatch(square) //发起'乘方'的action
console.log(store.getState()) //当前值为11*11=121

store.dispatch(add(2)) //发起'+2'的action
console.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.js
export const ADD = 'ADD'
export const SQUARE = 'SQUARE'
export const SET = 'SET'

// action/math.js
import { 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.js
import { 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.js
import 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)

　　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.js
import { 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.js
import 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)

【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.js

// action/fetch.js
import { 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.js

// action/math.js
import { 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.js

// constants/ActionTypes.js
export 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.js

// reduce/fetch.js
import { 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.js

// index.js
import 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)

 

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.js
import 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

　　详细代码如下所示，且可访问github线上地址

【components】

// components/Math.js
import 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.js
import { 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.js

// actions/fetch.js
import { 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.js

// actions/math.js
import { 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.js
export 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.js

// reducers/fetch.js
import { 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.js

// reducers/index.js
import { combineReducers } from 'redux'
import math from './math'
import fetch from './fetch'
const rootReducer = combineReducers({
  math,
  fetch
})

export default rootReducer

reduces/math.js

// reduces/math.js
import { 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.js
export const getFetchMessage = state => state.fetch.message
export const getFetchIsShow = state => state.fetch.isShow

// selectors/math.js
export const getNum = state => state.math

【根目录】

index.js

// index.js
import 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.js

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

转自：http://www.cnblogs.com/xiaohuochai/p/8447826.html

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