Objective-C class names with +

Question

Does the class name, for example UIImage+Something or UIImageView+Somethingelse , do it act as a custom UIImage or UIImageView ?

Answer 1

I think you are looking at category file names, not classes. The plus sign + not valid in class names or any other identifier in Objective-C.

The Objective-C category is a way of adding methods (but not instance variables) to a class to which you do not necessarily have a source. For example, if you often want to create inverted copies of UIImages, you can use the category to add the upsideDownImage method to the upsideDownImage class.

This code is usually stored in a file called UIImage+UpsideDown.m (with an accompanying header file, UIImage+UpsideDown.h ).

Answer 2

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