Swift AppDelegate如何知道要显示什么视图？

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let initialViewController = storyboard.instantiateInitialViewController()
    window?.rootViewController = initialViewController
    window?.makeKeyAndVisible()
    return true
}

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    let viewController = ViewController()
    window?.rootViewController = viewController
    window?.makeKeyAndVisible()
    return true
}