我无法在 app.js 中设置上下文状态,我以某种方式在其中获得空值,但可以在子组件中访问它。
我想在用户访问页面时在 app.js 中设置上下文状态,以便我可以在整个应用程序中使用它,例如根据用户是否登录显示不同的标题
根据请求的沙盒 URL -> https://codesandbox.io/s/quizzical-snyder-2qghj?file=/src/App.js https://codesandbox.io/s/quizzical-snyder-2qghj?file=/src/App.js
我正在关注https://upmostly.com/tutorials/how-to-use-the-usecontext-hook-in-react https://upmostly.com/tutorials/how-to-use-the-usecontext-hook-in-react
app.js
// import installed dependencies
import React, { useEffect, useContext } from 'react';
import { BrowserRouter as Router, Switch, Route } from 'react-router-dom';
// import custom contexts
import { AuthContext, AuthContextProvider } from './contexts/auth/AuthContext';
// import pages
import Homepage from './pages/homepage/Homepage';
// import components
import Footer from './components/footer/Footer';
import Header from './components/header/Header';
export default function App() {
const [authState, setAuthState] = useContext(AuthContext);
useEffect(() => {
console.log(authState); // prints *{}*
console.log(setAuthState); // prints *() => {}*
const token = localStorage.getItem('token');
const tokenIsExpired = parseInt(localStorage.getItem('tokenIsExpired'));
if (!tokenIsExpired && token.length) {
setAuthState({
userIsLoggedin: true,
fName: 'test fname',
lName: 'test lname',
userName: 'testname'
});
} else {
setAuthState({
userIsLoggedin: false,
fName: '',
lName: '',
userName: ''
});
}
if (tokenIsExpired) {
localStorage.setItem('token', '');
}
}, [authState, setAuthState]);
return (
<Router>
<AuthContextProvider value={[authState, setAuthState]}>
<div className='App'>
<Header />
<Switch>
<Route exact path='/'>
<Homepage />
</Route>
</Switch>
<Footer />
</div>
</AuthContextProvider>
</Router>
);
}
AuthContext.js
import React, { useState, createContext } from 'react';
const AuthContext = createContext([{}, () => {}]);
const AuthContextProvider = (props) => {
const [authState, setAuthState] = useState({
userIsLoggedin: false,
fName: '',
lName: '',
userName: ''
});
return (
<AuthContext.Provider value={[authState, setAuthState]}>
{props.children}
</AuthContext.Provider>
);
};
export { AuthContext, AuthContextProvider };
使用AuthCOntext.js
import { useContext } from 'react';
import { AuthContext } from './AuthContext';
const useAuthContext = () => {
const [authState, setAuthState] = useContext(AuthContext);
const login = (loginDetails) => {
setAuthState({
userIsLoggedin: true,
fName: 'test fname',
lName: 'test lname',
userName: 'testname'
});
};
const logout = () => {
setAuthState({
userIsLoggedin: false,
fName: '',
lName: '',
userName: ''
});
};
return { login, logout };
};
export default useAuthContext;
header.js
// import installed dependencies
import React, { useContext, useEffect } from 'react';
// import components
import LoggedOutHeader from './logged-out-header/LoggedOutHeader';
import LoggedInHeader from './logged-in-header/LoggedInHeader';
// import custom contexts
import { AuthContext } from '../../contexts/auth/AuthContext';
const Header = () => {
const [authState, setAuthState] = useContext(AuthContext);
console.log(authState); //prints *{userIsLoggedin: false, fName: "", lName: "", userName: ""}*
console.log(setAuthState); //prints *ƒ dispatchAction(fiber, queue, action) {...*
const header = authState.isUserLoggedIn ? (
<LoggedInHeader />
) : (
<LoggedOutHeader />
);
return header;
};
export default Header;