Customize error message in NSTextField with NSNumberFormatter

Question

I'm working on a little project to learn Objectiv-C. Now I run into a problem:

I had create a Cocoa application with a NSTextField with NumberFormatter. Now, if the user clicks on the text field an try to insert some stuff like "asd" he hears an error peep.

But I want to give the user some future information about the error, maybe with an panel or something like that. How can I receive this error message an can add my own functions?

Thanks for your help

Answer 1

There should be a callback from any method of NSNumberFormatter that returns YES/NO.

Even if it does not have, subclass it and add your own method.