import UIKitclass ViewController: UIViewController , UIAlertViewDelegate {@IBOutlet var label: UILabel?@IBOutlet var btn: UIButton?@IBAction func btnClick(AnyObject) {    showAlert()}func showAlert() {    let alert = UIAlertView()    alert.title = "Alert"    alert.delegate = self    alert.message = "Hello Apple"    alert.addButtonWithTitle("OK")    alert.addButtonWithTitle("Cancel")    alert.show()}override func viewDidLoad() {    super.viewDidLoad()    // Do any additional setup after loading the view, typically from a nib.}override func didReceiveMemoryWarning() {    super.didReceiveMemoryWarning()    // Dispose of any resources that can be recreated.}func alertView(alertView: UIAlertView!, clickedButtonAtIndex buttonIndex: Int) {    switch buttonIndex        {    case 0:        self.label?.text = "ok";    case 1:        self.label?.text = "cancel"    default:        println("alertView cancel!")    }}}