“Unrecognized selector sent to instance” in swift

I have no idea what I am doing wrong. I am also quite new to programming so I am not very good at debugging. This was a test app so that I can see how swift ties in with app development. So far, I have got this:

class ViewController: UIViewController, UITextViewDelegate {

    var textView: UITextView!

    init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) {
        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        var widthField = self.view.bounds.size.width - 10
        var heightField = self.view.bounds.size.height - 69 - 221
        var textFieldString: String! = ""
        //Set up text field
        self.textView = UITextView(frame: CGRectMake(5, 64, widthField, heightField))
        self.textView.backgroundColor = UIColor.redColor()
        self.view.addSubview(self.textView)
        //Set up the New button
        var newButtonString: String! = "New Note"
        var heightButton = 568 - heightField - 1000
        let newButton = UIButton(frame: CGRect(x: 5, y: 5, width: widthField, height: 50)) as UIButton
        UIButton.buttonWithType(UIButtonType.System)
        newButton.setTitle(newButtonString,forState: UIControlState.Normal)
        newButton.backgroundColor = UIColor.redColor()
        newButton.addTarget(self, action: "buttonAction:", forControlEvents: UIControlEvents.TouchUpInside)
        self.view.addSubview(newButton)

    }

    func buttonAction() {
        println("tapped button")
    }
}

I am getting the error “Unrecognized selector sent to instance” when I press the button in the iOS simulator. The app opens fine but whenever the button is pressed, it just crashes.