DisplayAler.swift

extension UIApplication {
    class func topViewController(base: UIViewController? = UIApplication.sharedApplication().keyWindow?.rootViewController) -> UIViewController? {
        if let nav = base as? UINavigationController {
            return topViewController(nav.visibleViewController!)
        }
        if let tab = base as? UITabBarController,
            let selected = tab.selectedViewController {
                return topViewController(selected)
        }
        if let presented = base?.presentedViewController {
            return topViewController(presented)
        }
        return base
    }
}


// Generic Alert with OK Button
// From Andrei Naechaev

func displayAlert(title: String, message: String, okAction: ((UIAlertAction)->Void)?) {
    if let topController = UIApplication.topViewController() {
        
        let alertController = UIAlertController(title: title, message: message, preferredStyle: .Alert)
    
        let okAction = UIAlertAction(title: "OK", style: .Default, handler: okAction)
        alertController.addAction(okAction)
    
        topController.presentViewController(alertController, animated: true, completion: nil)
    }
}