React中react-redux的使用以及redux-thunk异步操作案例

当我们使用redux的时候，可能会出现不同组件中有很多重复的redux代码，官方给我们封装了一个react-redux来解决这个问题

现在实现这样一个效果，点击减，数量变化

第一步肯定就是安装了

yarn add react-redux

创建组件

about.js

import React, { PureComponent } from 'react'
import {connect} from 'react-redux'

import {
  subAction,
  getHomeMultidataAction
} from '../store/actionCreators'

class about extends PureComponent  {
  render(){
    return (
      

        

        
about
        
当前:{this.props.counter}
        this.props.decreament()}>-1
        this.props.removenumber(5)}>-5
      
    )
  }
}

const mapStateToProps = state =>{
  return {
    counter:state.counter,
    banners:state.banners,
    recommends:state.recommends
  }
};

const mapDispachToProp = dispatch =>{
  return {
    decreament(){
      dispatch(subAction(1))
    },
    removenumber(num){
     dispatch(subAction(num))
    },
    getHomeMultidata(){
      dispatch(getHomeMultidataAction)
    }
  }
};

export default connect(mapStateToProps,mapDispachToProp)(about)

创建一个store文件夹，专门放redux代码

index.js

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


export default store

reducer.js

import {
  SUB_NUMBER,
} from './constants.js'

const defaultState = {
  counter: 0,
}

function reducer(state = defaultState, action) {
  switch (action.type) {
    case SUB_NUMBER:
      return { ...state, counter: state.counter - action.num }
    default:
      return state
  }
}

export default reducer

constants.js

export const SUB_NUMBER = "SUB_NUMBER"

actionCreators.js

import {
  SUB_NUMBER,
} from './constants.js'

export const subAction = num =>({
  type:SUB_NUMBER,
  num
})

这样就好了，当我们在别的组件里面就不用写类似这样的代码了

constructor(props){
    super(props);
    this.state={
      counter:store.getState().counter
    }
  }
  //订阅
  componentDidMount(){
   this.unsubscribe =  store.subscribe(()=>{
      this.setState({
        counter:store.getState().counter
      })
    })
  }
  //取消订阅
  componentWillUnmount(){
   this.unsubscribe()
  }

再来说一下redux-thunk

当我们有从接口请求的数据需要存储到redux中时候，我们可以直接在redux发送网络请求，相当于一个中间件，当我们请求的时候可以做一些事，类似expree和koa

首先安装

yarn add redux-thunk

在主index.js中

import {Provider} from 'react-redux'

ReactDOM.render(
  
    
  
,document.querySelector('#root'))

在上面创建的store中的index.js中这样写

import {createStore,applyMiddleware} from 'redux'
import thunkMiddleware from 'redux-thunk'

import reducer from './reducer.js'

//应用一些中间件
const storeEnhancer =  applyMiddleware(thunkMiddleware)

const store = createStore(reducer,storeEnhancer)


export default store

actionCreators.js中

import axios from 'axios'

import {
  CHANGE_BANNERS
} from './constants.js'

export  const getHomeMultidataAction = dispatch =>{
   axios({
       url:'',
     }).then((res)=>{
       console.log(res)
       dispatch(changeBannersAction(data))
     })
}

constants.js

export const CHANGE_BANNERS = "CHANGE_BANNERS"

reducer.js

import {
  CHANGE_BANNERS
} from './constants.js'

const defaultState = {
  banners:[]
}

function reducer(state = defaultState, action) {
  switch (action.type) {
    case CHANGE_BANNERS:
      return {...state,banners:action.banners}
    default:
      return state
  }
}

export default reducer

这样即可

在这我再说一下react-redux的怎么实现的

创建一个connect.js

import React,{ PureComponent } from "react"

import {StoreContext} from './context'

export function connect(mapStateToProps,mapDispachToProp){
  return function enhanceHOC(WrappedComponent){
    class EnhanceComponent extends PureComponent{
      constructor(props,context){
        super(props,context);
        this.state ={ 
          storeState:mapStateToProps(context.getState())
        }
      }
      componentDidMount(){
       this.unsubscribe =  this.context.subscribe(()=>{
          this.setState({
            storeState:mapStateToProps(this.context.getState())
          })
        })
      }
      componentWillUnmount(){
        this.unsubscribe()
      }
      render(){
        return 
      }
    }
    EnhanceComponent.contextType = StoreContext
    return EnhanceComponent
  }
}

创建一个context.js

import React from 'react'

const StoreContext = React.createContext()

export{
  StoreContext
}

在主index.js中

import {StoreContext}  from './learn-redux2/utils/context'
		
ReactDOM.render(
  

    
  
,document.querySelector('#root'))

其实react-redux就是这样实现的