redux

一个专门用于做状态管理的JS库，基本上与react配合使用

作用：集中式管理react应用中多个组件共享的状态

使用场景：

某个组件的状态，需要让其他组件可以随时拿到（共享）

一个组件需要改变另一个组件的状态（通信）

总体原则：能不用就不用，如果不用比较吃力才考虑使用

使用案例

纯react版本

import React, { Component } from 'react'

export default class Count extends Component {
    state = {
        count: 0
    }
    increment = () => {
        this.setState({
            count: this.state.count + this.selectNumber.value * 1
        })
    }
    decrement = () => {
        this.setState({
            count: this.state.count - this.selectNumber.value * 1
        })
    }
    incrementOdd = () => {
        if (this.state.count % 2 !== 0) {
            this.setState({
                count: this.state.count + this.selectNumber.value * 1
            })
        }
    }
    incrementAsync = () => {
        setTimeout(() => {
            this.setState({
                count: this.state.count + this.selectNumber.value * 1
            })
        }, 500)
    }
    render() {
        return (
            <div>
                <h1>当前求和为：{this.state.count}</h1>
                <select ref={c => this.selectNumber = c}>
                    <option value="1">1</option>
                    <option value="2">2</option>
                    <option value="3">3</option>
                </select>
                <button onClick={this.increment}>+</button>
                <button onClick={this.decrement}>-</button>
                <button onClick={this.incrementOdd}>奇数求和</button>
                <button onClick={this.incrementAsync}>异步加</button>
            </div>
        )
    }
}

App.js文件

import React from 'react'
import Count from './components/Count'
export default class App extends React.Component {
  render() {
    return (
      <div>
        <Count />
      </div>

    )
  }
}

redux精简版

store.js文件

//引入createStore 专门用于创建redux中最为核心的store对象
import { createStore } from 'redux'
//引入Count组件服务的reducer
import countReducer from './count_reducer'
const store = createStore(countReducer)
export default store

Count_reducer.js 文件

/*
该文件用于创建一个为Count组件服务的reducer，其本质就是一个函数
reducer函数会接到两个参数，分别为：之前的状态（prestate），动作对象（action）
*/
const initstate = 0
export default function countReducer(preState = initstate, action) {
    //从action对象中获取：type，data
    const { type, data } = action
    //根据type决定如何加工数据
    switch (type) {
        case 'increment':
            return preState + data
        case 'decrement':
            return preState - data
        default:
            return preState
    }
}

import React, { Component } from 'react'
import store from '../../redux/store'
export default class Count extends Component {
    state = {
        // count: 0
    }
    // componentDidMount() {
    //     //检测redux中状态的变化，只要变化，就调用reder
    //     store.subscribe(() => {
    //         this.setState({})
    //     })
    // }
    increment = () => {
        store.dispatch({
            type: 'increment',
            data: this.selectNumber.value * 1
        })
    }
    decrement = () => {

        store.dispatch({
            type: 'decrement',
            data: this.selectNumber.value * 1
        })

    }
    incrementOdd = () => {
        const count = store.getState()
        if (count % 2 !== 0) {
            store.dispatch({
                type: 'increment',
                data: this.selectNumber.value * 1
            })
        }
    }
    incrementAsync = () => {
        setTimeout(() => {
            store.dispatch({
                type: 'increment',
                data: this.selectNumber.value * 1
            })
        }, 500)
    }
    render() {
        return (
            <div>
                <h1>当前求和为：{store.getState()}</h1>
                <select ref={c => this.selectNumber = c}>
                    <option value="1">1</option>
                    <option value="2">2</option>
                    <option value="3">3</option>
                </select>
                <button onClick={this.increment}>+</button>
                <button onClick={this.decrement}>-</button>
                <button onClick={this.incrementOdd}>奇数求和</button>
                <button onClick={this.incrementAsync}>异步加</button>
            </div>
        )
    }
}

import React from 'react';
import ReactDOM from 'react-dom/client';
import App from './App';
import store from './redux/store'
const root = ReactDOM.createRoot(document.getElementById('root'));

root.render(<App />);

store.subscribe(() => {
    root.render(<App />);
})

一般对象如Object {}:为同步

函数对象如function：为异步

所谓异步action是指返回一个函数