首发自我的github博客,迎接star
注:如要运转本文的代码,请先确认本身的react版本已支撑hooks
react hooks出来已经有段时刻了,本文不对hooks的详细用法作引见,而是运用hooks完成一个浅易的基于context的redux
运用useReducer完成第一版redux
React hooks自带了useReducer供我们运用,它接收两个参数,一是reducer函数,二是初始state,并返回state和dispatch函数,以下
const [state, dispatch] = useReducer(reducer, initialState);
这个函数本身完成的话也不难,以下:
const useMyReducer = (reducer, initialState) => {
const [state, setState] = useState(initialState);
const dispatch = action => {
const newState = reducer(action, state);
setState(newState);
};
return [state, dispatch];
};
行将initialState作为state的初始状况传入useState,dispatch则是一个函数,它会将接收的action和state传给reducer,并猎取reducer的返回值赋给state
我们先应用useReducer完成一个计数器的简朴页面
reducer函数和initialState以下:
const initialState = {
count: 0
};
const reducer = (state, action) => {
switch (action.type) {
case "increase":
return { ...state, count: state.count + 1 };
case "decrease":
return { ...state, count: state.count - 1 };
default:
return state;
}
};
计数器组件:
const Demo = () => {
const [state, dispatch] = useReducer(reducer, initialState);
return (
<div>
counter:{state.count}
<div>
<button
onClick={() => {
dispatch({ type: "increase" });
}}
>
increase
</button>
<button
onClick={() => {
dispatch({ type: "decrease" });
}}
>
decrease
</button>
</div>
</div>
);
};
这就是第一版的redux了,但这个redux有些题目,就是它的state和dispatch是属于本身的,其他组件并不能拿到,也就是说,假如我们的页面有两个Demo组件,它们的state是各自自力,互不影响的
将state和dispatch存在context中
为了处置惩罚上述题目,我们必需具有一个全局状况,并将state和dispatch放入这个全局状况中。这里,我们选用context作为我们的全局状况,context在旧版React中不引荐运用,但在革新以后,官方最先引荐人人运用
我们先建立一个context:
const context = React.createContext();
为了各个组件都能拿到context的数据,我们须要有一个Provider组件包在最外层:
const Provider = props => {
const [state, dispatch] = useReducer(reducer, initialState);
return (
<context.Provider value={{ state, dispatch }}>
{props.children}
</context.Provider>
);
};
我们将useReducer返回的state、dispatch传入context.Provider中,让它的children都能拿到
然后,我们像下面一样用Provider包在组件外层:
<Provider>
<Demo />
<Demo />
</Provider>
我们删去计数器Demo组件中的:
const [state, dispatch] = useReducer(reducer, initialState);
加上经由过程useContext函数拿到context上的数据:
const { state, dispatch } = useContext(context);
要注意的是,传入useContext函数的context必需是我们之前经由过程React.createContext()
建立的context
如许,即使是两个Demo组件,它们也是共用一份数据了
处置惩罚异步的题目
很显然,如今的context-redux和纯真的redux一样,只能dispatch一个对象,也就是说,这个dispatch操纵是同步的,假如我们要做异步的操纵呢?很简朴,我们自创redux-thunk的要领,让dispatch能够接收函数参数
革新Provider函数组件以下:
const Provider = props => {
const [state, origin_dispatch] = useReducer(reducer, initialState);
const dispatch = action => {
if (typeof action === "function") {
return action(origin_dispatch);
}
return origin_dispatch(action);
};
return (
<context.Provider value={{ state, dispatch }}>
{props.children}
</context.Provider>
);
};
我们将userReducer函数返回的原始dispath命名为origin_dispatch
,自定义dispatch函数,当action为函数的时刻,我们实行action函数,并将origin_dispatch
看成参数传进去;action不是函数,直接挪用origin_dispatch
,不做处置惩罚
我们测试一下:
const sleep = wait => {
return new Promise(resolve => {
setTimeout(() => resolve(), wait);
});
};
const increaseCount = async dispatch => {
await sleep(1000);
dispatch({ type: "increase" });
};
<button
onClick={() => {
dispatch(increaseCount);
}}
>
increase
</button>
increaseCount
是一个异步函数,我们将它看成参数传入我们封装的新dispatch中,点击increase按钮,1s以后,计数器的数字加1,至此,我们的context-redux也支撑dispatch异步操纵了
末了
本文的代码,我放在了本身的github上,这是传送门