Weird bindings issue

Question

I'm trying to use a browser view with bindings to represent some data and I'm getting an error message:

2008-11-11 17:22:28.636 BrowserViewTest[18269:813] Cocoa Bindings: Error accessing value
 for key path arrangedObjects.projects of object <NSTreeController: 0x1321e0>[object class: BillingCode] 
(from bound object <NSBrowser: 0x126930> with object ID 0 in Nib named MainMenu.nib): 
[<_NSControllerTreeProxy 0x128630> valueForUndefinedKey:]: this class is not key 
value coding-compliant for the key displayString.
2008-11-11 17:22:28.638 BrowserViewTest[18269:813] Brow view cont awakeFromNib
2008-11-11 17:22:28.639 BrowserViewTest[18269:813] project count: 0

As shown by the NSLog output, this happens even before awakeFromNib is called in my app controller, and even though I know that BillingCode is KVC compliant for displayString.

It seems to be related to the value set for "Class" under my Tree Controller->Attributes->Object Controller, as if I change the name of that Class the name in the error message changes with it. The weird thing is as far as I know there shouldn't be any objects in the content array at that point, as I don't add them till awakeFromNib gets called.

Answer 1

It almost sounds like the type of object currently in your dictionary is not of the type you expect it to be, so the runtime can't get a value for the key displayString I'd try to figure out when an object is added to your dictionary, and then from there figure out why it isn't of the type that you expect it to be.