What does the text inside parentheses in @interface and @implementation directives mean?

Question

I\'ve got a very basic question about some sample code from Apple. In the .m file, the class declarations look like this:

@interface MyMovieViewController (O         


        

Answer 1

Those are "categories".

With those you can extend any objective-C class by adding methods, which will apply to all the objects of the class.

More detailed article here: http://macdevelopertips.com/objective-c/objective-c-categories.html