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[英]UseSelector returns undefined even the state is updated correctly
[英]useSelector hook first returns undefined state and after an action call returns the state correctly
我是 React 鈎子的新手,我嘗試將我的項目與 redux 集成,問題是在我用於登錄的 function 組件中,當我嘗試使用 useSelector 獲取我的 initialState 屬性時,Z9ED39E2EA931588EF73E 是 undefinedA931588B6A9
import React, {useState} from 'react';
import loginStyles from './login.module.css';
import {useDispatch , useSelector, shallowEqual} from 'react-redux';
import {login} from '../../store/actions/actions';
export default (props) => {
const initialState = {
"email":'',
"password":''
}
const dispatch = useDispatch();
const [loginForm, setValue] = useState(initialState);
const changeValue = (event) => {
const name = event.target.name;
const value = event.target.value;
setValue(prevState => {
return {
...prevState,
[name]: value
}
});
}
useSelector((state) => {
console.log(state)
});
return (
<article className={loginStyles.main}>
<aside className={loginStyles.left}>
</aside>
<aside className={loginStyles.right}>
<div>
<input name="email" onChange={(event) => changeValue(event) } type = "text" value = {loginForm['email']} />
<input name="password" onChange={(event) => changeValue(event) } type = "text" value = {loginForm['password']} />
<button onClick={() => dispatch(login("jared", true))} >clicl</button>
</div>
</aside>
</article>
);
}
在我單擊按鈕后,它會打印出正確的 state 但首先渲染它會打印出未定義的內容。 那我應該修改什么?
這是我的代碼的 rest。 謝謝你。
應用程序.js
import React from 'react';
import {Provider} from 'react-redux';
import { createStore } from 'redux';
import reducer from './store/reducer';
import Layout from './layouts/main';
import './app.css';
function App() {
const store = createStore(reducer);
return (
<Provider store={store}>
<Layout />
</Provider>
);
}
export default App;
import React from 'react';
import {Provider} from 'react-redux';
import { createStore } from 'redux';
import reducer from './store/reducer';
import Layout from './layouts/main';
import './app.css';
function App() {
const store = createStore(reducer);
return (
<Provider store={store}>
<Layout />
</Provider>
);
}
export default App;
import React from 'react';
import {Provider} from 'react-redux';
import { createStore } from 'redux';
import reducer from './store/reducer';
import Layout from './layouts/main';
import './app.css';
function App() {
const store = createStore(reducer);
return (
<Provider store={store}>
<Layout />
</Provider>
);
}
export default App;
減速器.js
const initialState = {
logged: false,
user: null,
empresas: null
}
const reducer = (state = initialState, action) => {
switch(action.type) {
case 'ONLOGIN': {
return {
...state,
user:action.user,
logged: true
}
}
case 'ONLOGOUT': {
return {
...state,
user: null,
logged: false
}
}
}
}
export default reducer;
動作.js
const login = (user, logged)=> {
return {
type:'ONLOGIN',
user: user,
logged: true
}
}
export {login}
您需要在首次加載時獲取存儲 state 以獲取初始 state。
動作.js
const fetchState = () => {
return {type: 'FETCH_STATE'}
}
減速器.js
const reducer = (state = initialState, action) => {
switch(action.type) {
case 'ONLOGIN': {
return {
...state,
user:action.user,
logged: true
}
}
case 'ONLOGOUT': {
return {
...state,
user: null,
logged: false
}
}
case 'FETCH_STATE': {
return {
...state,
}
}
default:
return state;
}
}
最后在組件中,您需要在首次加載時使用React.useEffect
或componentDidMount
獲取 state
import React, {useState} from 'react';
import loginStyles from './login.module.css';
import {useDispatch , useSelector, shallowEqual} from 'react-redux';
import {login} from '../../store/actions/actions';
export default (props) => {
const initialState = {
"email":'',
"password":''
}
const dispatch = useDispatch();
const [loginForm, setValue] = useState(initialState);
React.useEffect(() => {
dispatch(fetchState())
},[])
// remaining code
上面的代碼工作正常。 我自己運行上面的代碼並使用 useSelector 成功獲取了 initialState 屬性。
{記錄:真實,用戶:“jared”,empresas:null} 記錄:真實用戶:“jared” empresas:null。
您的項目中可能存在問題,例如
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