content: import React from 'react';
  import {Link} from 'react-router';
  
  export default class Header extends React.Component {
    render(){
      return (
        <nav className="navbar navbar-default">
          <div className="container-fluid">
            <div className="navbar-header">
              <button type="button" className="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
                <span className="sr-only">Toggle navigation</span>
                <span className="icon-bar"></span>
                <span className="icon-bar"></span>
                <span className="icon-bar"></span>
              </button>
              <a className="navbar-brand" href="#">简单论坛系统</a>
            </div>
            <div className="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
              <ul className="nav navbar-nav">
                <li className="active">
                  <Link to="/">首页</Link>
                </li>
                <li><a href="#">帮助</a></li>
              </ul>
              <ul className="nav navbar-nav navbar-right">
                <li><a href="#">Link</a></li>
                <li className="dropdown">
                  <a href="#" className="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span className="caret"></span></a>
                  <ul className="dropdown-menu">
                    <li><a href="#">Action</a></li>
                    <li><a href="#">Another action</a></li>
                    <li><a href="#">Something else here</a></li>
                    <li role="separator" className="divider"></li>
                    <li><a href="#">Separated link</a></li>
                  </ul>
                </li>
              </ul>
            </div>
          </div>
        </nav>
      )
    }
  }
  