gistfile1.txt

func application(_ application: UIApplication, supportedInterfaceOrientationsFor window: UIWindow?) -> UIInterfaceOrientationMask {
    if let rootViewController = self.topViewControllerWithRootViewController(rootViewController: window?.rootViewController) {
      if (rootViewController.responds(to: Selector(("canRotate")))) {
        // Unlock landscape view orientations for this view controller
        return .allButUpsideDown;
      }
    }
    
    // Only allow portrait (standard behaviour)
    return .portrait;
  }
  
  private func topViewControllerWithRootViewController(rootViewController: UIViewController!) -> UIViewController? {
    if (rootViewController == nil) { return nil }
    if (rootViewController.isKind(of: UITabBarController.self)) {
      return topViewControllerWithRootViewController(rootViewController: (rootViewController as! UITabBarController).selectedViewController)
    } else if (rootViewController.isKind(of: UINavigationController.self)) {
      return topViewControllerWithRootViewController(rootViewController: (rootViewController as! UINavigationController).visibleViewController)
    } else if (rootViewController.presentedViewController != nil) {
      return topViewControllerWithRootViewController(rootViewController: rootViewController.presentedViewController)
    }
    return rootViewController
  }