When to use Categories Objective-C?
ios, objective-c, objective-c-category, oop
Solution
A category is an extension of a class, not of a specific instance of a class. And, any modification that a category makes to a class is available to all subclasses (as with other methods on classes in OOP).
So, if you add a category on `NSObject`, basically all classes in your entire app have access to the methods in that category - hence you need to be very careful what methods you add there.
Whether you add a category or a helper class is personal preference in a lot of cases, both will work.
Problem
If I have a method to attach an animation to an `UI Element`, instead of copy/pasting the code for this method into many `viewcontrollers`, can I just create one `class` to hold the method and then import it? I assume it doesn't make sense to use a `category` in this instance because I need this method in multiple `viewcontrollers`, and a `category` is an extension of a single `viewcontroller`.