ios swift Button, Label, AlertView

import UIKit

class 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!")
    }
}
}