Swift + AppDelegate

 var window: UIWindow?

    var navigationC: UINavigationController?

//    var loginVC:LoginVC!

    var welcomeVC:WelcomeVC!

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

            welcomeVC = WelcomeVC(nibName: "WelcomeVC", bundle: nil)

            self.navigationC  = UINavigationController(rootViewController: welcomeVC!)

        self.window?.rootViewController = navigationC

        self.navigationC!.setNavigationBarHidden(true, animated: true)

        self.window?.backgroundColor = UIColor.white

        self.window?.makeKeyAndVisible()

        return true

}