UIAlertViewDelegate method clickedButtonAtIndex not getting called when implementing my own delegate

I'd like to popup an alert from different ViewControllers. Because I wanted to handle whether the user clicked "OK" or "Cancel" consistently, I decided to implement my own UIAlertViewDelegate and call it from my UIViewController.

The problem is that willDismissWithButtonIndex, didDismissWithButtonIndex, and clickedButtonAtIndex are never called when I click "OK" or "Cancel". I know that my delegate is getting used, because willPresentAlertView() and didPresentAlertView() are getting called when the alert displays.

Here is the code for my delegate:

import UIKit

class AlertViewDelegate: NSObject, UIAlertViewDelegate {
    func willPresentAlertView(alertView: UIAlertView) {
        println("will present")
    }

    func didPresentAlertView(alertView: UIAlertView) {
        println("did present")
    }

    func alertViewCancel(alertView: UIAlertView) {
        println("cancelled")
    }

    func alertView(alertView: UIAlertView, willDismissWithButtonIndex buttonIndex: Int) {
        println("will dismiss")
    }

    func alertView(alertView: UIAlertView, didDismissWithButtonIndex buttonIndex: Int) {
        println("did dismiss")
    }

    func alertView(alertView: UIAlertView, clickedButtonAtIndex buttonIndex: Int) {
        println("clicked")
    }
}

And here is the code for my ViewController:

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        var delegate = AlertViewDelegate()
        var alert = UIAlertView(title: "alert", message: "blah blah", delegate: delegate, cancelButtonTitle: "cancel", otherButtonTitles: "OK")
        alert.show()
    }

}

What am I doing wrong?

this variable 'var delegate = AlertViewDelegate()' deallocated at end of scope so nothing called, try move delegate to property