receiver type *** for instance message is a forward declaration

Question

In my iOS5 app, I have NSObject States class, and trying to init it:

states = [states init];

here is init

Answer 1

FWIW, I got this error when I was implementing core data in to an existing project. It turned out I forgot to link CoreData.h to my project. I had already added the CoreData framework to my project but solved the issue by linking to the framework in my pre-compiled header just like Apple's templates do:

#import 

#ifndef __IPHONE_5_0
#warning "This project uses features only available in iOS SDK 5.0 and later."
#endif

#ifdef __OBJC__
    #import 
    #import 
    #import 
#endif