content: import React, { Component } from 'react';
  import './App.css';
  import logo from './mini_logo.png';
  
  import {
    BrowserRouter as Router,
    Route,
    Link
  } from 'react-router-dom';
  
  import {
    Home, 
    Product, 
    Purchase, 
    PurchaseDetail, 
    Sale,
    SaleDetail,
    Inventory,
    Settings,
    Printer,
    Upgrade
  } from './components';
  
  class App extends Component {
    render() {
      return (
        <Router>
          <div>
            <div className="navbar">
              <div className="container">
                <div className="App-toolbar" >
                  <ul className="commander">
                    <li className="btn-grad"><Link to="/">首页</Link></li>
                    <li className="btn-grad"><Link to="/product">货品</Link></li>
                    <li className="btn-grad"><Link to="/purchase">采购</Link></li>
                    <li className="btn-grad"><Link to="/sale">销售</Link></li>
                    <li className="btn-grad"><Link to="/inventory">库存</Link></li>
                    <li className="btn-grad"><Link to="/settings">设置</Link></li>
                    <li className="btn-grad"><Link to="/printer">打印</Link></li>
                    <li className="btn-grad"><Link to="/upgrade">更新</Link></li>
                  </ul>
                </div>
              </div>
            </div>
            <div className="App">
              <div className="App-header">
                <img src={logo} className="App-logo" alt="logo" />
                <h2 className="App-Brand">数据同步器</h2>
              </div>
              <Route exact path="/" component={Home}/>
              <Route exact path="/product" component={Product}/>            
              <Route exact path="/purchase" component={Purchase}/>
              <Route exact path="/purchase/:code" component={PurchaseDetail}/>
              <Route exact path="/sale" component={Sale}/>
              <Route exact path="/sale/:code" component={SaleDetail}/>
              <Route exact path="/inventory" component={Inventory}/>
              <Route exact path="/settings" component={Settings}/>
              <Route exact path="/printer" component={Printer}/>
              <Route exact path="/upgrade" component={Upgrade}/>
            </div>
          </div>
        </Router>
      );
    }
  }
  
  export default App;
  