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'));