Question

Using different frameworks in my projects I have often faced with custom elements which created as class inherit from NSObject (correct me if something is wrong). What are the main rules of creating such UI elements?

Answer 1

NSObject is the very basic class in Cocoa. It is responsible for the most basic things that every class needs, like memory management. (Almost) all classes in Cocoa inherit from NSObject and you usually subclass NSObject if you want to implement a model class.

If you want to create your own GUI element, you should subclass UIView or UIControl. UIView will give you capabilities to do custom drawing, handling touch events and others. UIControl (which itself is a UIView subclass) adds functionality for control elements which the user can interact with, like UITextField, UISlider etc. This is what you should subclass if you plan to implement a custom control.