Objective-C class names with a +

Question

Does a class name, say UIImage+Something or UIImageView+Somethingelse, mean that it acts like a custom UIImage or UIImageView?

Answer 1

I think you are looking at the file names of Categories, not Classes. The plus character + is not allowed in class names or any other identifier in Objective-C.

An Objective-C category is a way of adding methods (but not instance variables) to a class you don't necessarily have the source to. For example, if you frequently want to make upside-down copies of UIImages, you can use a category to add a upsideDownImage method onto the UIImage class.

It's common to save this code in a file named UIImage+UpsideDown.m (with an accompanying header file, UIImage+UpsideDown.h).

Answer 2

This is a naming convention when using an Objective-C Category to extend the functionality of a class. See the article: http://macdevelopertips.com/objective-c/objective-c-categories.html for a much better explanation.