react-router4 嵌套路由的使用方法

import React from 'react';import ReactDOM from 'react-dom';import { HashRouter as Router, Route, Switch} from 'react-router-dom';import createBrowserHistory from 'history/createBrowserHistory';import UserAddPage from './pages/UserAdd/index';import HomePage from './pages/Home/index';import HomeLayout from './components/HomeLayout/index';const hashHistory = createBrowserHistory();const NoMatch = ({ location }) => ( <div>  <h3>无法匹配 <code>{location.pathname}</code></h3> </div>)ReactDOM.render(( <Router history={hashHistory}>  <div>   <HomeLayout>//总会加载这个组件，并且下面 swicth 里面的组件会在它里面 render     <Switch>     <Route path="/" exact component={HomePage}/>     <Route path="/user/add" component={UserAddPage}/>     <Route component={NoMatch}/>    </Switch>   </HomeLayout>  </div> </Router>), document.getElementById('root'));