Swift NSNotification crash

AppDelegate.swift

//
//  AppDelegate.swift
//  emailRegexTest
//
//  Created by <#Stan Serebryakov#> on 20/02/15.
//

import UIKit

@UIApplicationMain
@objc class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func validateEmail(text: String) -> Bool {
        let emailRegEx = "^[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,4}$" // http://www.regular-expressions.info/email.html
        let emailRange = text.uppercaseString.rangeOfString(emailRegEx, options: .RegularExpressionSearch)
        return emailRange != nil
    }

    @objc func textDidChange(notification: NSNotification) -> Void {
        if let tf = notification.object as? UITextField {
            print(validateEmail(tf.text))
        }
        return
    }

    func application(app: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

        let f = UIScreen.mainScreen().bounds
        window = UIWindow(frame: f)

        var vc = UIViewController()
        vc.view = UIView(frame: f)
        vc.view.backgroundColor = .greenColor()
        var tf = UITextField(frame: CGRect(x: 10, y: 10, width: 100, height: 50))
        tf.backgroundColor = .redColor()
        vc.view.addSubview(tf)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("textDidChange:"),
            name: UITextFieldTextDidChangeNotification, object: tf)

        window?.rootViewController = vc
        window?.makeKeyAndVisible()

        return true
    }
}

Screenshot.png

I'm not sure how I came across this now, but have you tried just removing the "-> Void" and the return statement from the notification handler?