Problem with the ButtonTap Action

[douth]

Hey there I've got a problem. I wana get a Alertdialog which comes when a Button was tapped and shows the result of a computation. The button got the ID "berechneButton". I tried something but in won't work.
This is my code:

In the Setup Assistant:

Code:

Mojo.Event.listen(this.controller.get("berechneButton"),Mojo.Event.tap, this.handleEvents.bind(this, "ergebnis"));

My Event (Alert) which should started after the button got tapped:

Code:

SceneAssistant.prototype.ergebnis = function(event) {
   
    this.controller.showAlertDialog({
        title: $L("Ergebnis"),
        message: $L(" €"),
        });

}

What I'm doing wrong? Where is the mistake?

And another question is it possible to display a result of a formula in the message attribut of the AlertDialog?

Thanks a lot for your help!!