manageObjectContext throwing unrecognized selector errors?

My application is a typical non-document based core data application. I have modified none of the pre-provided project code and have been using the AppDelegate files that Xcode provides by default (the project's not large enough to warrant much more).

Now, when I try to add an item to one of my core data stores with

NSManagedObject *colorItemObject = [NSEntityDescription insertNewObjectForEntityForName:@"ColorItem" inManagedObjectContext: [NSApp managedObjectContext]];
    [colorItemObject setValue:[colorSetsArrayController valueForKeyPath:@"selection.colorSetName"] forK开发者_运维问答ey:@"parent"];

it throws an unrecognized selector exception:

-[_NSStateMarker managedObjectContext]: unrecognized selector sent to instance 0x100118290

Similar errors occur from using [self managedObjectContext]. What could be causing this?

I'm pretty sure

 [NSApp managedObjectContext]

does not return a valid managedObjectContext. Have you made a category to NSApplication with a method called managedObjectContext? If not, change that to

[self managedObjectContext]

and it should work. (I assumed your code is inside your app delegate.)