error with import <cocoa/cocoa.h>

Question

I added class files from another project to my new iPhone Window for the first time. The class is a simple class that defines a polygon, and subclasses NSObject. As part of the standard template for an Objective C class, this class definition imports Cocoa.h

#import <Cocoa/Cocoa.h>

However, just by adding this class, I'm getting an error that

Cocoa/Cocoa.h:No such file or directory.

I don't understand this because the exact same line occurs in another class definition (the controller) within the same project.

Answer 1

Subclasses of NSObject (at least on the iPhone) do not import the Cocoa.h header. Instead, they import Foundation.h:

#import <Foundation/Foundation.h>