The other day, I was working on JustLooking, changing the appearance and the like of a couple of dialogs. As I ran the programs and went to show the dialogs (“panels” in the local terminology), nothing would show and I’d get an error in my XCode results window:

"Unknown class 'CustomCombo' in nib file. using 'NSObject' instead."

I spent the next half hour trying to figure out why Interface Builder didn’t know about this class: it was there in the class inspector, and the ui widgets were correctly set up to use that new class, and all the hookups in the UI also seemed correct.

Well, I finally figured out: when I first developed the class, I had some errors in it, but wanted to test a few things out in my program elsewhere. So I had unchecked it in XCode, telling the IDE not to compile and link it.

Thus, when Cocoa tried to load the NIB file, it couldn’t find the definition for the class, and just put in NSObject instead.

Here’s to hoping that this blog entry saves somebody that 30 minutes I spent on that one.