Question

Possible Duplicate:
How can I have references between two classes in Objective-C?
Objective-C #import loop

I’m getting a couple errors in my code and I’m not sure but I think its because I’m #importing an interface inside another interface where I’m #importing the other interface. If I’m confusing you I’ll give you an example.

#import "OneClass.h"

@interface SecondClass : NSObject
{
    OneClass * obj;
}

#import "SecondClass.h"

@interface OneClass : NSObject
{
    SecondClass * obj;
}

Answer 1

Yes, you have a circular import. The problem here is that the second import (the one that re-imports your first header) is basically ignored by the compiler, since it thinks it’s already imported that header.

The solution here is to use @class forward-declarations instead of using #imports. Not only does this solver the circular import problem, but it’s a better idea anyway since it breaks unnecessary dependency chains (e.g. if I edit OneClass.h, SecondClass.h won’t need to be re-processed).

To apply this here, simply remove the #import OneClass.h in SecondClass.h and replace it with @class OneClass;

In the more general case, you don’t ever need to #import a header file just to declare an ivar/property/method that uses a class from that header. The @class token is sufficient. You do, however, need to #import the header file if you’re inheriting from the class, or if you’re referencing another non-class type declared in that header. Also remember that if you use @class in your header, you need to remember to put the actual #import into your .m file.