redux-thunk、redux-saga、react-redux中间件的使用

demo源码： `https://github.com/recall-lidemin/todolist-demo.git`

什么是Redux中间件？

redux中间件的中间指的是action和store中间
redux中间件实际是对dispatch方法的封装或升级，升级之后，dispatch就既能接收对象，也能接收函数
补充：中间件指的是redux的中间件，不是react的。

1.redux-thunk

安装redux-thunk yarn add redux-thunk
注册中间件,使用applyMiddleware

import { createStore, applyMiddleware, compose } from 'redux'
import thunk from 'redux-thunk'
import reducer from './reducer'

// 为了thunk与devtools一起使用
const composeEnhancers = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__
 ? window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__({})
 : compose
const enhancer = composeEnhancers(applyMiddleware(thunk))
const store = createStore(reducer, enhancer)

export default store

在action中使用，使用了redux-thunk中间件之后，action返回就可以是一个函数，不再必须是对象，在这个函数中，我们可以发起异步请求来获取数据,而且返回的函数会被注入dispatch这个参数，我们不再需要引入store

store/actionCreators.js

export const getTodoList = () => {
  return async (dispatch) => {
    const res = await axios.get('http://localhost:3000/list')
    const action = initListAction(res.data)
    dispatch(action)
  }
}

在页面组件中

import {getTodoList} from './store/actionCreators'
const TodoList = () => {
  // 发送请求获取数据
  const getList = async () => {
    const action = getTodoList()
    store.dispatch(action) // 注入dispatch
  }
}

2.redux-saga

安装redux-saga yarn add redux-saga
注册redux-saga

import { createStore, applyMiddleware, compose } from 'redux'
import createSagaMiddleware from 'redux-saga'
import reducer from './reducer'
import mySaga from './sagas'

// 创建saga中间件
const sagaMiddleware = createSagaMiddleware()
// 开启devtools
const composeEnhancers = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__
  ? window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__({})
  : compose
// 注册saga
const enhancer = composeEnhancers(applyMiddleware(sagaMiddleware))
const store = createStore(reducer, enhancer)
// 运行saga文件
sagaMiddleware.run(mySaga)

export default store

在saga.js中使用

import { call, put, takeEvery, takeLatest } from 'redux-saga/effects'
import { GET_INIT_LIST } from './actionTypes'
import { initListAction } from './actionCreators'
import axios from 'axios'

// 处理函数，可以在此进行异步请求，这里使用的es6的Genegetor函数
function* fetchList() {
  try {
    const res = yield axios.get('http://localhost:3000/list')
    const action = initListAction(res.data)
    yield put(action)
  } catch (error) {
    // do null
  }
}
// 监听页面action的派发，执行对应的函数
function* mySaga() {
  yield takeEvery(GET_INIT_LIST, fetchList)
}

export default mySaga

在页面组件中分发，触发saga监听

  // 使用redux-saga
  const getList = async () => {
    const action = getTodoList()
    store.dispatch(action)
  }

3.react-redux

安装react-redux yarn add react-redux
创建store

import { createStore } from 'redux'
import reducer from './reducers'

const store = createStore(reducer)

export default store

连接react-redux,使用Provider,注册到上下文

import React from 'react'
import ReactDOM from 'react-dom'
import 'antd/dist/antd.css'
import TodoList from './todolist'
import { Provider } from 'react-redux'
import store from './react-redux'

// react-redux连接store
ReactDOM.render(
  <React.StrictMode>
    <Provider store={store}>
      <TodoList />
    </Provider>
  </React.StrictMode>,
  document.getElementById('root')

在组件中通过connect使用

import React from 'react'
import { Button, Input, List } from 'antd'
import { connect } from 'react-redux'

const TodoList = (props) => {
  const { inputValue, list, handleChange, handleAdd, handleDel } = props

  return (
    <>
      <div style={{ display: 'flex' }}>
        <Input
          style={{ width: 200 }}
          value={inputValue}
          onChange={handleChange}
        />
        <Button type="primary" onClick={handleAdd}>
          提交
        </Button>
      </div>
      <List
        size="large"
        bordered
        dataSource={list}
        renderItem={(item, index) => (
          <List.Item key={item} onClick={() => handleDel(index)}>
            {item}
          </List.Item>
        )}
      />
    </>
  )
}

// 将state映射到props中
const mapStateToProps = (state) => {
  return {
    inputValue: state.inputValue,
    list: state.list,
  }
}
// 将dispatch映射到props中，可以在此处写处理函数，也可以将dispatch从组件props中解构出来，直接在组件中进行dispatch分发，此处就可以不必写，只传一个mapStateToProps参数即可
const mapDispatchToProps = (dispatch) => {
  return {
    handleChange(e) {
      dispatch({
        type: 'change_input_value',
        value: e.target.value,
      })
    },
    handleAdd() {
      dispatch({
        type: 'add_list',
      })
    },
    handleDel(index) {
      dispatch({
        type: 'del_list',
        value: index,
      })
    },
  }
}

export default connect(mapStateToProps, mapDispatchToProps)(TodoList)