show UIAlertController outside of ViewController

Question

I have trouble to display my UIAlertController because I'm trying to show it in a Class which is not an ViewController.

I already tried adding it:

 var alertController = UIAlertController(title: "Title", message: "Message", preferredStyle: .Alert)

UIApplication.sharedApplication().keyWindow?.rootViewController?.presentViewController(alertController, animated: true, completion: nil)

Which is not working... I didn't find any solution that worked for me yet.

Answer 1

I wrote this extension over UIAlertController to bring back show().
It uses recursion to find the current top view controller:

extension UIAlertController {

    func show() {
        present(animated: true, completion: nil)
    }

    func present(#animated: Bool, completion: (() -> Void)?) {
        if let rootVC = UIApplication.sharedApplication().keyWindow?.rootViewController {
            presentFromController(rootVC, animated: animated, completion: completion)
        }
    }

    private func presentFromController(controller: UIViewController, animated: Bool, completion: (() -> Void)?) {
        if let navVC = controller as? UINavigationController,
            let visibleVC = navVC.visibleViewController {
                presentFromController(visibleVC, animated: animated, completion: completion)
        } else
        if let tabVC = controller as? UITabBarController,
            let selectedVC = tabVC.selectedViewController {
                presentFromController(selectedVC, animated: animated, completion: completion)
        } else {
            controller.presentViewController(self, animated: animated, completion: completion);
        }
    }
}

Now it's as easy as:

var alertController = UIAlertController(title: "Title", message: "Message", preferredStyle: .Alert)
alertController.show()

EDIT:

For Xcode 8.0 & Swift 3:

extension UIAlertController {

    func show() {
        present(animated: true, completion: nil)
    }

    func present(animated: Bool, completion: (() -> Void)?) {
        if let rootVC = UIApplication.shared.keyWindow?.rootViewController {
            presentFromController(controller: rootVC, animated: animated, completion: completion)
        }
    }

    private func presentFromController(controller: UIViewController, animated: Bool, completion: (() -> Void)?) {
        if let navVC = controller as? UINavigationController,
            let visibleVC = navVC.visibleViewController {
            presentFromController(controller: visibleVC, animated: animated, completion: completion)
        } else
            if let tabVC = controller as? UITabBarController,
                let selectedVC = tabVC.selectedViewController {
                presentFromController(controller: selectedVC, animated: animated, completion: completion)
            } else {
                controller.present(self, animated: animated, completion: completion);
        }
    }
}