redux的使用(跨组件传值)

0、基本概念

store  就是保存数据的地方,将store看成一个容器,一个应用只能有一个store
//如何生成一个store  createStore

//store--index.js
import { createStore } from 'redux'
const defaultState = {
    msg:"react很不好用"
}
const reducer = (state=defaultState,action)=>{
    return state;
}
// createStore只能接收函数
let store = createStore(reducer);
export default store;

reducer 就是对state重新计算的过程就是reducer,reducer必须是函数

1、安装依赖

yarn add redux

2、项目配置

store
    --index.js
    --reducer.js

2-1、创建store容器，管理数据

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

2-2、创建reducer，接收action，重新计算state

//reducer.js
let defaultState = {
    msg:"react"
}
export default (state=defaultState,action)=>{
    return state
}

3-1、在Home.js中导入store（需要在哪里使用就在哪里导入）

import store from '../store'js
class Home extends Component {
    constructor(props) {
        super(props);
        this.state = getState();
    }
    ....
}

3-2、action(View发出的一个通知，要改变state)

//通过一个事件派发action
1.创建一个ation,同时派发
class Home extends Component {
    ...
    render() {
        return (
            <div>
                <button onClick={this.handleClick}>改变store</button>
            </div>
        );
    }
    handleClick=()=>{
        const action = {
            type:"btn_change",
            value:"复习redux"
        }
        store.dispatch(action)
    }
}
export default Home;

//2.store自动接收action,之后将action传递给reducer

//3.在reducer改变state
let defaultState = {
    msg:"react"
}
//reducer可以接收state,但是不能直接修改state，所以这里做一个深拷贝
export default (state=defaultState,action)=>{
      //看数据派发过来没有
    console.log(action)
    switch(action.type){
        case "btn_change":
            var newState = {...state};
            newState.msg = action.value;
            return newState;
        default:
            return state;
    }
}

//4.订阅store的状态的改变,只要store改变,store.subscribe(fn),fn函数必然会执行
class Home extends Component {
    constructor(props) {
        ...
        store.subscribe(this.handleStoreChange);
    }
    ...
    handleStoreChange=()=>{
        console.log(1)
        this.setState(store.getState())
    }
}