XCode 4.2 why do I see @interface both inside .h and .m files

Question

why do I see @interface twice( inside .h and .m files in this UIViewController files I've created. the one in the .m seems to be like a constructor. is it?

.h file

@interface BlackTimer : UIViewController 


@end

.m file

@interface ViewController ()

@end

possible duplicate of [Difference between @interface definition in .h and .m file](http://stackoverflow.com/questions/3967187/difference-between-interface-definition-in-h-and-m-file) — jscs, Jun 07 '12 at 19:36

score 7 · Answer 1 · answered Jun 07 '12 at 08:38

7

usually in the .m file you put all the declarations for private methods

it's a good use to write the word "private" (or something similar) like this:

@interface ViewController (private)

-(void)myPrivateMethod;

@end

answered Jun 07 '12 at 08:38

meronix

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Here is another SO question related to your comment. – pasawaya Jun 07 '12 at 08:42
Better: no name for that category at all, as you will have a class extension than, what will work better with the compiler. see qegals answer. – vikingosegundo Jun 07 '12 at 11:24

pasawaya · Answer 2 · 2012-09-22T20:10:14.253

7

The @interface in the .m file is called a class extension. Here is a good link explaining it. Hope this helps. And here is the Apple documentation on class extensions.

edited Sep 22 '12 at 20:10

answered Jun 07 '12 at 08:38

pasawaya

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score -1 · Answer 3 · answered Jun 07 '12 at 08:39

-1

The @interface ViewController () definition in the implementation file (.m) is an anonymous Category. It allows to define ivars, properties and messages your class implements without exposing them to other objects importing your public interface (.h).

answered Jun 07 '12 at 08:39

Luca Corti

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XCode 4.2 why do I see @interface both inside .h and .m files

3 Answers3