我试图为应用程序需要的所有组件创建一个共享的全局状态，而不是依赖 props 钻孔或 redux，我试图用 React Context 来实现。

为什么当我在路由之间切换时我的用户上下文不存在？下面的应用程序说明了这个问题。

我需要结合使用任何其他钩子useContext吗？

//index.js
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import { AuthenticationProvider }  from "./AuthenticationProvider";

const Index = () => {
    return (
      <AuthenticationProvider>
        <App />
      </AuthenticationProvider>
    );
}

ReactDOM.render(<Index />, document.getElementById('root'));

//App.js
import React, { useState, useContext } from 'react';
import { BrowserRouter as Router, Route, Switch } from "react-router-dom";
import './App.css';
import { AuthenticationContext } from './AuthenticationProvider';

function AddUser() {

  const [formUser, setFormUser] = useState("");

  const [user, setUser] = useContext(AuthenticationContext);

  const handleSubmit = async (event) => {
    event.preventDefault();
    setUser(formUser);
  }

  return (
    <React.Fragment>
      Form user: {formUser}.
          <form id="form1" onSubmit={handleSubmit}>
        <input type="text" id="user" onChange={event => setFormUser(event.target.value)} />
        <input type="submit" value="Save" />
      </form>
      <br/>
      Current user: {user}
      <br/>
      <a href="/">Back to home</a>
    </React.Fragment>
  );
}

function Home() {

  const [user, setUser] = useContext(AuthenticationContext);

  return (
    <React.Fragment>
      <div className="App">
        Hello {user}.
        <br/>
        <a href="/add">Add user</a>
    </div>
    </React.Fragment>
  );
}

function App() {
  return (
    <Router>
      <Switch>
        <Route exact path="/" component={Home} />
        <Route exact path="/add" component={AddUser} />
      </Switch>
    </Router>
  );
}

export default App;

//AuthenticationProvider.js
import React, { useState, createContext } from "react";

const DEFAULT_STATE = "";

export const AuthenticationContext = createContext(DEFAULT_STATE);

export const AuthenticationProvider = ({ children }) => {
  const [user, setUser] = useState(DEFAULT_STATE);

  return (
    <AuthenticationContext.Provider value={[user, setUser]} >
      {children}
    </AuthenticationContext.Provider>
  );
}