Hooks 提供了很多好用的api，甚至很多人认为Hooks的useReducer等Api已经可以取代Redux了。其实Hooks和Redux的使用场景并不冲突，而且可以互相借鉴，最近react-edux最新版本(7.1)也引入了Hooks风格的Api。

useState和useReducer是Hooks中最常用的Api，适合用来进行简单的状态管理，但也都有一些无法满足的需求

useState

import React, { useState } from "react";

const ComponentUseState = () => {
  const [num, setNum] = useState(0);

  return (
    <div>
      <h2>Using useState</h2>
      Number: {num}
      <button onClick={() => setNum(num + 1)}>+</button>
      <button onClick={() => setNum(num - 1)}>-</button>
    </div>
  );
};

export default ComponentUseState;

useState可以用最简单的方式更新状态，但是状态更新的逻辑（例如上面例子中的加减一运算）散落在UI中，不能独立复用，也不便于测试。

useReducer

使用useReducer可以解决上面useState无法解决的问题。

import React, { useReducer } from 'react'

const initialState = {num: 0};

const reducer = (state, action) => {
  switch(action.type) {
    case 'decrement':
      return {...state, num: state.num - 1}
    case 'increment':
      return {...state, num: state.num + 1}
    default:
      return state;
  }
}

const ComponentUseReducer = () => {
  const [state, dispatch] = useReducer(reducer, initialState)

  const { num } = state
  return (
    <div>
      <h2>Using useReducer</h2>
      Number: {num}
      <button onClick={() => dispatch({type: 'increment'})}>+</button>
      <button onClick={() => dispatch({type: 'decrement'})}>-</button>
    </div>
  );
};

export default ComponentUseReducer;

可以看到useReducer的逻辑脱离了UI，可以独立复用。reducer就是一个单纯的Js方法，我们可以对reducer进行单独测试，甚至可以在chrome中进行调试

实际使用中reducer应该以单独的文件存在，上面例子为了简单起见放到了一起。

useReducer虽然很好地分离了逻辑和UI，但是无法像redux一样进行跨组件的状态共享，例如子组件无法方便的访问到num

useSelector、useDispatch

如上所述，Hooks仍然无法替代Redux的作用，特别是在状态共享方面。庆幸的是 react-redux 7.1之后也可以使用useSelector、useDispatch等HooksApi替代connect，减少模板代码。

import React from "react";
import { createStore } from "redux";
import { Provider, useSelector, useDispatch } from "react-redux";

const initialState = { num: 0 };

const reducer = (state, action) => {
  switch (action.type) {
    case "decrement":
      return { ...state, num: state.num - 1 };
    case "increment":
      return { ...state, num: state.num + 1 };
    default:
    
      return state;
  }
};

const store = createStore(reducer, initialState);

const ComponentUseReactRedux = () => {
  return (
    <div>
      <h2>ComponentUseReactRedux</h2>
      <Provider store={store}>
        <ChildComponentUseReactRedux />
      </Provider>
    </div>
  )
}

const ChildComponentUseReactRedux = () => {
  const num = useSelector(state => state.num);
  const dispatch = useDispatch();
  return (
    <div>
      <h3>Using useSelector, useDispatch</h3>
      Number: {num}
      <button onClick={() => dispatch({ type: "increment" })}>+</button>
      <button onClick={() => dispatch({ type: "decrement" })}>-</button>
    </div>
  );
};

export default ComponentUseReactRedux;

createStore

通过createStore将state存入store，

const store = createStore(reducer, initialState);

再通过Provider向子组件暴露store，通过store在父子组件之间共享状态

 <Provider store={store}>
     <ChildComponentUseReactRedux />
 </Provider>

useSelector

子组件可以通过useSelector访问name

  const num = useSelector(state => state.num);

当然，也可以提出selector函数，方便替换和复用，如下

const selector = state => {
  return state.num;
}

const num = useSelector(selector);

useDispatch

通过useDispatch 可以获取dispatch

  const dispatch = useDispatch()

即使多几个子组件也可以共享状态

const ComponentUseReactRedux = () => {
  return (
    <div>
      <h2>ComponentUseReactRedux</h2>
      <Provider store={store}>
        <ChildComponentUseReactRedux />
        <ChildComponentUseReactRedux />
      </Provider>
    </div>
  )
}

最后

通过useSelector、useDispatch等方法，我们可以用Hooks方法完成Redux的功能，Hooks和Redux之间没有替代关系，应该更好地共存和融合。