如何使用Swift 3以编程方式在所有视图控制器中显示选项卡栏？

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // 创建UITabBarController实例
    let tabBarController = UITabBarController()
    
    // 设置视图控制器数组
    let viewController1 = ViewController1()
    let viewController2 = ViewController2()
    let viewController3 = ViewController3()
    
    tabBarController.viewControllers = [viewController1, viewController2, viewController3]
    
    // 设置选项卡栏的标题和图标
    viewController1.tabBarItem = UITabBarItem(title: "Tab 1", image: UIImage(named: "tab1"), tag: 0)
    viewController2.tabBarItem = UITabBarItem(title: "Tab 2", image: UIImage(named: "tab2"), tag: 1)
    viewController3.tabBarItem = UITabBarItem(title: "Tab 3", image: UIImage(named: "tab3"), tag: 2)
    
    // 设置UITabBarController为根视图控制器
    window?.rootViewController = tabBarController
    
    return true
}