以编程方式创建 Tab Bar 控制器而不使用 Storyboard

class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    
    var firstTabNavigationController : UINavigationController!
    var secondTabNavigationControoller : UINavigationController!
    var thirdTabNavigationController : UINavigationController!
    var fourthTabNavigationControoller : UINavigationController!
    var fifthTabNavigationController : UINavigationController!
    

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        Fabric.with([Crashlytics.self])
        
       window = UIWindow(frame: UIScreen.main.bounds)
        
        
        window?.backgroundColor = UIColor.black
            
        
        let tabBarController = UITabBarController()
        
        firstTabNavigationController = UINavigationController.init(rootViewController: FirstViewController())
        secondTabNavigationControoller = UINavigationController.init(rootViewController: SecondViewController())
        thirdTabNavigationController = UINavigationController.init(rootViewController: ThirdViewController())
        fourthTabNavigationControoller = UINavigationController.init(rootViewController: FourthViewController())
        fifthTabNavigationController = UINavigationController.init(rootViewController: FifthViewController())
        
        tabBarController.viewControllers = [firstTabNavigationController, secondTabNavigationControoller, thirdTabNavigationController, fourthTabNavigationControoller, fifthTabNavigationController]
        
        
        let item1 = UITabBarItem(title: "Home", image: UIImage(named: "ico-home"), tag: 0)
        let item2 = UITabBarItem(title: "Contest", image:  UIImage(named: "ico-contest"), tag: 1)
        let item3 = UITabBarItem(title: "Post a Picture", image:  UIImage(named: "ico-photo"), tag: 2)
        let item4 = UITabBarItem(title: "Prizes", image:  UIImage(named: "ico-prizes"), tag: 3)
        let item5 = UITabBarItem(title: "Profile", image:  UIImage(named: "ico-profile"), tag: 4)

        firstTabNavigationController.tabBarItem = item1
        secondTabNavigationControoller.tabBarItem = item2
        thirdTabNavigationController.tabBarItem = item3
        fourthTabNavigationControoller.tabBarItem = item4
        fifthTabNavigationController.tabBarItem = item5
                
        UITabBar.appearance().tintColor = UIColor(red: 0/255.0, green: 146/255.0, blue: 248/255.0, alpha: 1.0)
        
        self.window?.rootViewController = tabBarController
        
        window?.makeKeyAndVisible()

        return true
    }