react-router 路由嵌套 以及路由无限循环

App.js:

import React, { Component } from 'react';
import { BrowserRouter as Router, Route, Link } from "react-router-dom";
import './App.css';
//定义组件的三种方式
// 1
class Home extends Component{
  render(){
    return (
        <div>这里是主页</div>
      );
  }
}
// 路由嵌套(和路由变量)可以让多个路由对应一个组件
class News2 extends Component{
  
  render(){
    console.log(this.props.match.params.gxx)
    return (
      <Router>
        <div>
          <Link to={this.props.match.url+'/run'}>跑步</Link>
          <Link to={this.props.match.url+'/swim'}>游泳</Link>
          <Link to={this.props.match.url+'/photo'}>照相</Link>
          <Route path={this.props.match.url+'/:name'} component={News2} />
        </div>
      </Router>
    )
  }
}
class News extends Component{
  render(){
    /*可通过this.props.match.url获取父级的路由地址*/
    console.log(this.props.match.url); /*/News*/
    return (
      <Router>
          <div>
           { /*<Link to='/News/run'>跑步</Link>
            <Link to='/News/swim'>游泳</Link>
            <Link to='/News/photo'>照相</Link>*/
            /*可改写为*/}
            {/*<Link to={this.props.match.url+'/run'}>跑步</Link>
            <Link to={this.props.match.url+'/swim'}>游泳</Link>
            <Link to={this.props.match.url+'/photo'}>照相</Link>
            <Route path='/News/:gxx' component={Sport}/>*/}
          {/*路由循环嵌套*/}
            <Link to={this.props.match.url+'/run'}>跑步</Link>
            <Link to={this.props.match.url+'/swim'}>游泳</Link>
            <Link to={this.props.match.url+'/photo'}>照相</Link>
            <Route path='/News/:gxx' component={News2}/>
          </div>
      </Router>
    )
  }
}
class Sport extends Component{
/*path='/News/:gxx' 这里的参数可以在后面的Sport组件中通过this.props.match.params.gxx获取*/
 /*点击对应子路由获得参数run,swim,photo*/ 
  render(){
    return (
      <div>这是一项运动</div>
    )
  }
}
//3 普通函数(中获取路由相关信息)
const About = function(data){
  console.log(data.match.url)/*/About*/
  return (
      <div>这里是关于信息</div>
    )
}
class App extends Component {
  render() {
    return (
      /*路由要用Router标签包起来*/
      <Router>
        {/*要有一个根元素*/}
        <div>
          {/*to后为地址相对于当前地址而言*/}
          <Link to='/'>首页</Link>
          <Link to='/News'>新闻</Link>
          <Link to='/About'>关于</Link>
          {/*对应内容放在Route中 path为对应路径  component为对应组件 exact为严格匹配，只匹配路径为'/'的元素*/}
          <Route exact path='/' component={Home} />
          <Route path='/News' component={News} />
          <Route path='/About' component={About} />
        </div>
      </Router>
    );
  }
}

export default App;