前端学习--React(3)-编程知识

一、Redux

集中状态管理工具，不需要react即可使用，每个store的数据都是独立于组件之外的

vue小链接：vuex/pinia

基本使用

Redux将数据修改流程分成三个概念，state、action和reducer

state - 一个对象存放我们管理的数据状态

action - 一个对象描述你如何修改数据

reducer - 一个函数根据action的描述生成新的state

<button id="decrement">-</button>
<span id="count">0</span>
<button id="increment">+</button><script src="https://unpkg.com/redux@latest/dist/redux.min.js"></script><script>// 1. 定义reducer函数 // 作用: 根据不同的action对象，返回不同的新的state// state: 管理的数据初始状态// action: 对象 type 标记当前想要做什么样的修改function reducer (state = { count: 0 }, action) {// 数据不可变：基于原始状态生成一个新的状态 所以要返回新对象if (action.type === 'INCREMENT') {return { count: state.count + 1 }}if (action.type === 'DECREMENT') {return { count: state.count - 1 }}return state}// 2. 使用reducer函数生成store实例const store = Redux.createStore(reducer)// 3. 通过store实例的subscribe订阅数据变化// 回调函数可以在每次state发生变化的时候自动执行store.subscribe(() => {console.log('state变化了', store.getState())document.getElementById('count').innerText = store.getState().count})// 4. 通过store实例的dispatch函数提交action更改状态 const inBtn = document.getElementById('increment')inBtn.addEventListener('click', () => {// 增store.dispatch({type: 'INCREMENT'})})const dBtn = document.getElementById('decrement')dBtn.addEventListener('click', () => {// 减store.dispatch({type: 'DECREMENT'})})// 5. 通过store实例的getState方法获取最新状态更新到视图中</script>

react中使用redux

相关工具

Redux Toolkit 简化redux书写逻辑

react-redux 链接Redux和React的中间件

npm i @reduxjs/toolkit react-redux

安装成功

目录创建

创建src/store，modules存放子模块

counterStore.js

//1 导入并创建store
import {createSlice} from "@reduxjs/toolkit"const counterStore = createSlice({name:'counter',// 初始状态initialState:{count:0},// 更新状态的方法reducers:{inscrement(state){state.count++},descrement(state){state.count --}}
})const {inscrement, descrement} = counterStore.actions
const reducer = counterStore.reducerexport{inscrement,descrement
}export default reducer

store/index.js

集成store/modules中所有子模块

import { configureStore } from "@reduxjs/toolkit";
import counterReducer from "./modules/counterStore"// 将子模块中的所有store合成一个根store方便访问
const store = configureStore({reducer:{counter:counterReducer,}
})export default store

src/index.js

import React from 'react';
import ReactDOM from 'react-dom/client';
import App from './App';
import store from "./store"
import { Provider } from 'react-redux';const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(// 通过react-redux提供的Provider 给组件注入store 使得redux定义的store能够被react组件使用<Provider store={store}><App /></Provider>
);

App.js

useDispatch() 通过这个来派发reducer修改状态

import { useSelector, useDispatch } from "react-redux";
import {inscrement, descrement} from "./store/modules/counterStore"
function App() {const { count } = useSelector(state => state.counter)const dispatch = useDispatch()return (<div className="App"><button onClick={() => dispatch(inscrement())}>+</button>{count}<button onClick={() => dispatch(descrement())}>-</button></div>);
}export default App;

然后就完成了：

进阶版-提交action时传参

counterStore.js

增加了一个addToNum函数

//1 导入并创建store
import {createSlice} from "@reduxjs/toolkit"const counterStore = createSlice({name:'counter',// 初始状态initialState:{count:0},// 更新状态的方法reducers:{inscrement(state){state.count++},descrement(state){state.count --},addToNum(state, action){// dispatch调用该方法时传入的参数就存放在action.payloadstate.count += action.payload}}
})const {inscrement, descrement, addToNum} = counterStore.actions
const reducer = counterStore.reducerexport{inscrement,descrement,addToNum
}export default reducer

App.js

增加了两个值，传入不同参数

import { useSelector, useDispatch } from "react-redux";
import {inscrement, descrement, addToNum} from "./store/modules/counterStore"
function App() {const { count } = useSelector(state => state.counter)const dispatch = useDispatch()return (<div className="App"><button onClick={() => dispatch(inscrement())}>+</button>{count}<button onClick={() => dispatch(descrement())}>-</button><button onClick={() => dispatch(addToNum(10))}>+ 10</button><button onClick={() => dispatch(addToNum(-10))}>- 10</button></div>);
}export default App;

再进阶版-异步状态操作

channelStore.js

import {createSlice} from '@reduxjs/toolkit'
import axios from 'axios'const channelStore = createSlice({name:'channel',initialState:{channelList:[]},reducers:{getChannels(state, action){state.channelList = action.payload}}
})const {getChannels} = channelStore.actions//单独写一个异步action的函数 异步操作处理完毕后再调用同步action修改状态
const getChannelList = () => {return async(dispatch) => {const res = await axios.get('http://geek.itheima.net/v1_0/channels')dispatch(getChannels(res.data.data.channels))}
}export {getChannelList}const reducer = channelStore.reducer
export default reducer

App.js

import { useSelector, useDispatch } from "react-redux";
import {inscrement, descrement, addToNum} from "./store/modules/counterStore"
import {getChannelList} from "./store/modules/channelStore"
import {useEffect} from 'react'
function App() {const { count } = useSelector(state => state.counter)const { channelList } = useSelector(state => state.channel)const dispatch = useDispatch()useEffect(()=> {dispatch(getChannelList())}, [dispatch])return (<div className="App"><button onClick={() => dispatch(inscrement())}>+</button>{count}<button onClick={() => dispatch(descrement())}>-</button><button onClick={() => dispatch(addToNum(10))}>+ 10</button><button onClick={() => dispatch(addToNum(-10))}>- 10</button><ul>{channelList.map(item => <li key={item.id}>{item.name}</li>)}</ul></div>);
}export default App;