完成了所有畫面後，需要切換畫面，這裡使用的是Tabbar。

TabBar

使用Tabbar之前，要先把每個畫面處理一下，然後放進Tabbar陣列裡。

        let rootVC1 = AlarmViewController(nibName: String(describing: AlarmViewController.self), bundle: nil)
        let navigationVC1 = UINavigationController(rootViewController: rootVC1)
        
        let rootVC2 = StopWatchViewController(nibName: String(describing: StopWatchViewController.self), bundle: nil)
        let navigationVC2 = UINavigationController(rootViewController: rootVC2)
        
        let rootVC3 = WorldClockViewController(nibName: String(describing: WorldClockViewController.self), bundle: nil)
        let navigationVC3 = UINavigationController(rootViewController: rootVC3)
        
        let rootVC4 = TimerViewController(nibName: String(describing: TimerViewController.self), bundle: nil)
        let navigationVC4 = UINavigationController(rootViewController: rootVC4)
        
        let MyTabBar = UITabBarController()
        
        let AlarmVC = navigationVC1
        AlarmVC.tabBarItem.image = UIImage(systemName: "clock")
        AlarmVC.tabBarItem.title = "鬧鐘"
        
        let StopWatchVC = navigationVC2
        StopWatchVC.tabBarItem.image = UIImage(systemName: "stopwatch")
        StopWatchVC.tabBarItem.title = "碼表"
        
        let WorldClockVC = navigationVC3
        WorldClockVC.tabBarItem.image = UIImage(systemName: "globe")
        WorldClockVC.tabBarItem.title = "世界時鐘"
        
        let TimerVC = navigationVC4
        TimerVC.tabBarItem.image = UIImage(systemName: "timer")
        TimerVC.tabBarItem.title = "計時器"
        
        MyTabBar.viewControllers = [AlarmVC, StopWatchVC, WorldClockVC, TimerVC]
        MyTabBar.selectedIndex = 0
    }

今天到這裡就結束啦，明天就能開始做別的東西了。