Objective-C and the Interface section

Hi all,

Please don't blow my head off if this is the wrong place to ask this question, but I haven't found a better place yet. If it's wrong, please let me know where I can repost this for best results. Thanks.

So I am learning Objective-C, and find that a lot of questions are easily resolved online or in a book somewhere, but I took a look inside of UIView.h and saw the sections:

@interface UIView(UIViewGeometry)
...
@end

and

@interface UIView(UIViewHierarchy)
...
@end

and don't really know for sure what these are. I have looked everywhere to see if I can find an explanation of the @interface declaration that uses open and clode parens, and can't find any discussion on that whatsoever. Can someone explain this to me?

Just curiosity at this point, but I would like to know in case I ever want to use this for some reason.
Thanks...
Bruce

You want to learn about Categories. I don't think we can add anything beyond the below links. The short answer is you use categories to add methods to an existing class where you don't need to add variables. This avoids the expense of subclassing where it isn't needed.

Cocoadevcentral's Learn Objective-C.

Apple's Introduction to The Objective-C Programming Language.