Can a category implement a protocol in Objective C?

Question

I have a category on NSDate and it would be convenient if it could implement a protocol I previously created. Is this possible? what's the correct syntax for this?

Francophobe

Answer 1

Yes, that's possible. The syntax is:

@interface NSDate (CategoryName) <ProtocolName>
@end

@implementation NSDate (CategoryName)
@end

Here's Apple's documentation on the topic.

It's also possible to do this using a class extension. I very much like this to privately conform to delegate protocols. Doing so hides the implementation detail of being some delegate of some class from the public interface and removes the dependency from the header.

Causeuse

Too bad there isn't a way to move the protocol declaration to the class category's implementation. – Rebus

@Rebus That's what class extensions are there for. – Causeuse

@bikram990 The document has been retired and is now in the legacy section. I updated the link. – Causeuse

unfortunately we can not declare instance variables in categories, that we might need for some delegate protocol implementations – Alleneallentown

@Alleneallentown You could do that using objc_setAssociatedObject :) – Stewardson