您是否尝试切换您rootViewController在application(_:didFinishLaunchingWithOptions:)

假设Mainstoryboard您有rootViewController：

if userIsNotLoggedIn {
    let storyboard = UIStoryboard(name: "Loginstoryboard", bundle: nil)
    let loginController = storyboard.instantiateViewControllerWithIdentifier("LoginNavigationController") as UINavigationController
    window?.rootViewController = loginController
}

要在登录后切换视图控制器，您可以执行以下操作：

func loggedIn() {
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let mainController = storyboard.instantiateViewControllerWithIdentifier("MainVC") as UIViewController
    let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
    appDelegate.window?.rootViewController = mainController
}