Question

I’m new to Objective-C and am looking through many examples to wrap my head around it.
I came across this code:

@interface ImagePickerHelper : NSObject <UIImagePickerControllerDelegate, UIPopoverControllerDelegate, UINavigationControllerDelegate>
  //Blah Blah
@end

@interface ImagePickerHelper ()
  //Blah Blah
@end

On googling, I came to know that they specify the superclass and delegates (about which, incidentally, I know zilch) after the interface name.

But why is the interface declared twice here?

Answer 1

No, it is not declared two times, it is a Class interface (an anonymous category) that it is created to hold methods that you want to keep private in your class, for methods that you don’t want other class to see or to interact with ..

People often declare a standard category with a name(usually “private”) to hold private methods, but
the main advantage of using an anonymous category over a named category is that the compiler will complain if you do not implement a method declared in the anonymous category.

I have noticed that it is created by default from XCode 4.3 onwards .

Putting methods into this extension Class it is like declaring private methods in Java or C++ …