ask() - Show an OK/Cancel modal box that works in both iOS 7 and iOS 8

ask.swift

/// Show an OK/Cancel modal box that works in both iOS 7 and iOS 8
func ask(title: String, #message: String, #completion: (answer: Bool) -> Void) {
    if nil != objc_getClass("UIAlertController".UTF8String) { // use UIAlertController
        let alertController = UIAlertController(title: title, message: message, preferredStyle: .Alert)
        let cancelAction = UIAlertAction(title: "Cancel", style: .Cancel, handler: { (action) -> Void in
            completion(answer: false)
        })
        let okayAction = UIAlertAction(title: "OK", style: .Default, handler: { (action) -> Void in
            completion(answer: true)
        })
        alertController.addAction(cancelAction)
        alertController.addAction(okayAction)
        UIApplication.topViewController()?.presentViewController(alertController, animated: true, completion: nil)
    }
    else { // use UIAlertView
        let alertView = SelfDelegatingBoolAlertView(title: title, message: message, completion: completion)
        alertView.show()
    }
}

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

class SelfDelegatingBoolAlertView: UIAlertView, UIAlertViewDelegate {

    var completion: (answer: Bool) -> Void

    init(title: String, message: String?, completion: (answer: Bool) -> Void) {
        self.completion = completion
        super.init(frame: CGRectZero)
        self.delegate = self
        self.title = title
        self.message = message
        addButtonWithTitle("Cancel")
        addButtonWithTitle("OK")
        cancelButtonIndex = 0
    }

    required init(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func alertView(alertView: UIAlertView, clickedButtonAtIndex buttonIndex: Int) {
        completion(answer: buttonIndex != alertView.cancelButtonIndex)
    }
}