转自:https://blog.csdn.net/vitaviva/article/details/104508139
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
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。
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
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;
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>
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);
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> ) }
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。