react&redux&hook

1.理解redux原理

https://juejin.im/post/5def4831e51d45584b585000#heading-12

http://www.imooc.com/read/72/article/1679

redux通过创建一个store仓库保存state，每个action通过创建actioncreator创建,修改state需要通过dispatch相应的action去触发相应的reducer去改变state;

redux库包含createStore;包含三个参数 reducer、initalState、enhance;创建一个store仓库

combinreducer 生成一个combine函数并通过闭包将reducer 以各自各state为key;对应的reducer为value的对象；dispatch时会循环遍历该对象，匹配到对应的action_type去改变state，并且根据hasChange是否true判断是否返回更改过的新对象达到immutable

applymiddlewares  返回一个符合enhance的函数；是通过增强dispatch方法实现插件

2.react-redux 容器组件链接

react-redux的provide、connect是利用react context实现的

参考：https://juejin.im/post/5a90e0545188257a63112977

 每个容器组件通过connect链接，connect函数的mapStateToProps会根据返回的state去添加订阅；只有该容器组件用到的state改变才会触发该组件重新渲染

https://www.cnblogs.com/geoffgu/p/6035910.html

//index.js
import React from "react";
import ReactDOM from "react-dom";
import App from "./App";
import {Provider} from "react-redux";

import { createStore,combineReducers } from "redux";

let reducerObj={
  name (state='',action){
    const {type,payload} =action;
    switch(type){
      case 'SET_NAME':
        return payload;
      default :
    }
    return state;
  },
  age (state='',action){
    const {type,payload} =action;
    switch(type){
      case 'SET_AGE':
        return payload;
      default :
    }
    return state;
  },
  count (state='',action){
    const {type,payload} =action;
    switch(type){
      case 'ADD_COUNT':
        return state+1;
      case 'SUBCTRACT_COUNT':
        return state-1;
      default :
    }
    return state;
  }
};
let store=createStore(combineReducers(reducerObj),{
  name:'penguin',
  age:30,
  count:0
});

//通过provider 注入生成的store仓库
ReactDOM.render(
    <Provider store={store}>
        <App/>
    </Provider>
  , document.getElementById("root")
);

/* eslint-disable no-console */
/* eslint-disable no-debugger */
import React from "react";
import { connect, useSelector, useDispatch } from "react-redux";
import { addCount, subtractCount } from "./action";

const Detail=(props)=>{
  const {name,age}=props;
  console.log('渲染了Detail');
  return (
      <div>
          <span>{age}</span>
          <span>{name}</span>
      </div>
  );
};
const PDetail=connect(
  function mapStateToProps (state, props) {
    let {name,gender,...rest}=state;
    return {name,gender};
  },
  function mapDispatchToProps (dispatch, props) {
    return { dispatch };
  }
)(Detail);



//利用react-redux 7.1新增的useSelector、useDispatch替代connect
const PCounter=(props)=>{
  const count=useSelector(state=>state.count);
  const dispatch=useDispatch();
  console.log('渲染了counter');
  return(
      <div>
          <span>{count}</span>
          <button onClick={()=>dispatch(addCount())}>+1</button>
          <button onClick={()=>dispatch(subtractCount())}>-1</button>
      </div>
  );
};


// const Counter1=(props)=>{
//   const {count,dispatch} = props;
//   console.log('渲染了counter1');
//   return(
//       <div>
//           <span>{count}</span>
//           <button onClick={()=>dispatch(addCount())}>+1</button>
//           <button onClick={()=>dispatch(subtractCount())}>-1</button>
//       </div>
//   );
// };
// const PCounter1=connect(
//   function mapStateToProps (state, props) {
//     let {count,...rest}=state;
//     return {count};
//   },
//   function mapDispatchToProps (dispatch, props) {
//     return { dispatch };
//   }
// )(Counter1);

const App=(props)=>{
  return (
      <div>
          <PDetail/>
          <PCounter/>
          {/* <PCounter1/> */}
      </div>
  );
};
export default App;