React learning 24 (redux asynchronous action)

1) Clear: Delayed actions do not want to be handed over to the component itself, but to action

2) When you need asynchronous action: you want to operate on the state, but the specific tasks are returned by asynchronous tasks

3) Specific coding:

A. Installation: npm i redux-thunk, and configure it in store,js, and need to introduce thunk and import

applyMiddleware middleware

B. The function to create an action does not return a general object, but a function, which writes an asynchronous task

C. After the asynchronous task has a result, distribute a synchronous action to actually operate the data

D. Remarks: It is not necessary to write asynchronous tasks. You can wait for the results of asynchronous tasks before distributing synchronous tasks.

action

store.js

/*
  该文件专门用于暴露一个store对象，整个应用只有一个store对象
*/

//引入createStore，专门用于创建redux中最为核心的store对象
import {createStore, applyMiddleware} from 'redux'

//引入为Count组件服务的reducer
import countReducer from './count_reducer'

//引入redux-thunk，用于支持异步action
import thunk from 'redux-thunk'

export default createStore(countReducer, applyMiddleware(thunk))

count_actions.js

/*
  该文件专门为count组件生成action对象
*/
import { INCREMENT, DECREMENT } from "./constant"
//完整写法
// function createIncrementAction(data) {
//   return {type:'increment', data }
// }
//简写形式
export const createIncrementAction = data =>( {type:INCREMENT, data })

//完整写法
// function createDecrementAction(data) {
//   return {type:'decrement', data}
// }
export const createDncrementAction = data =>( {type: DECREMENT, data })

//异步action，就是值action的返回值是函数，异步action一般都会调用同步action
//异步action不是必须要用的
export const createIncrementAsyncAction = (data, time) =>{
  return (dispatch) => {
    setTimeout(() => {
      dispatch(createIncrementAction(data))
    },time)
  }
}

count-index.jsx

import React, { Component } from 'react'
//引入store，用于获取redux中获取的状态
import store from '../../redux/store'
//引入actionCreator，专门用于创建action对象
import { createIncrementAction, createDncrementAction, createIncrementAsyncAction} from '../../redux/count_action'

export default class Count extends Component {
  state = {carName:'奔驰c63'}//  把状态交给reducer之后组件也可以有自己独用的状态

  increment = () => {
    const {value} = this.selectNum
    store.dispatch(createIncrementAction(value*1))
  }
  decrement = () => {
    const {value} = this.selectNum
    store.dispatch(createDncrementAction(value*1))
  }
  incrementOdd = () => {
    const {value} = this.selectNum
    const count = store.getState()
    if(count % 2 !== 0) {
      store.dispatch(createIncrementAction(value*1))
    }
  }
  incrementWait = () => {
    const {value} = this.selectNum
    store.dispatch(createIncrementAsyncAction(value*1, 500))
  }
  render() {
    return (
      <div>
        <h1>当前求和为：{store.getState()}</h1>
        <select ref={c => {this.selectNum = c}}>
          <option value="1">1</option>
          <option value="2">2</option>
          <option value="3">3</option>
        </select>&nbsp;
        <button onClick= {this.increment}>+</button>&nbsp;
        <button onClick= {this.decrement}>-</button>&nbsp;
        <button onClick= {this.incrementOdd}>当前求和为奇数再加</button>&nbsp;
        <button onClick= {this.incrementWait}>等一等再加</button>
      </div>
    )
  }
}