What is “category” in Objective-C?

Question

Possible Duplicate:
How does a category work in Objective-C?

I am just getting started with Objective-C and was wondering when and where am i supposed to use category in objective C. is it a class or a protocol? An explanatory example would be of great help. Thanks

Solution 1

A category allows you to add methods to an existing class—even to one for which you do not have the source.

Categories are a powerful feature that allows you to extend the functionality of existing classes without subclassing

Check the apple doc for the Category in Objective-C

Solution 2

There is a section in the Objective-C 2.0 programming Language document about Categories and Extensions.

As you are just getting started it's a good doc to have on hand to look things up.

There is also a section on Categories in the Cocoa Core Competencies document, which is easier to get started with, and also has a lot of useful information for the beginner.

Comments

[Alex Bitek]

Categories in Objective-C are similar to Ruby open classes and C# extension methods

[Basil Bourque]

That first link is now obsolete. Apple redirects to listing of documentation.

[Arc676]

Just want to report that the Category in ObjC link no longer exists.

[Jared Egan]

@Arc676 Categories definitely still exist.

[Hima]

Both links are expired now.

[mr5]

Official documentation: developer.apple.com/library/content/documentation/Cocoa/…