How to present UIAlertController when not in a view controller?

Question

Scenario: The user taps on a button on a view controller. The view controller is the topmost (obviously) in the navigation stack. The tap invokes a utility class method call

Answer 1

Swift 4+

Solution I use for years with no issues at all. First of all I extend UIWindow to find it's visibleViewController. NOTE: if you using custom collection* classes (such as side menu) you should add handler for this case in following extension. After getting top most view controller it's easy to present UIAlertController just like UIAlertView.

extension UIAlertController {

  func show(animated: Bool = true, completion: (() -> Void)? = nil) {
    if let visibleViewController = UIApplication.shared.keyWindow?.visibleViewController {
      visibleViewController.present(self, animated: animated, completion: completion)
    }
  }

}

extension UIWindow {

  var visibleViewController: UIViewController? {
    guard let rootViewController = rootViewController else {
      return nil
    }
    return visibleViewController(for: rootViewController)
  }

  private func visibleViewController(for controller: UIViewController) -> UIViewController {
    var nextOnStackViewController: UIViewController? = nil
    if let presented = controller.presentedViewController {
      nextOnStackViewController = presented
    } else if let navigationController = controller as? UINavigationController,
      let visible = navigationController.visibleViewController {
      nextOnStackViewController = visible
    } else if let tabBarController = controller as? UITabBarController,
      let visible = (tabBarController.selectedViewController ??
        tabBarController.presentedViewController) {
      nextOnStackViewController = visible
    }

    if let nextOnStackViewController = nextOnStackViewController {
      return visibleViewController(for: nextOnStackViewController)
    } else {
      return controller
    }
  }

}