If anyone is interested in a website to get an overview of how to program Objective-C controls, this O’Reilly site looks pretty good:
It is actually geared towards Swift but also contains Objective-C code and found it organized in a way that I could find better what I needed to know about create in a UIControl than initially searching through Apple’s documentation. The site is quite old but it still looks like it gives programmers a good initial understanding of each control that they can go look up the updated specifics on the Apple documentation website.
The site is a an excerpt from a book; I’ll look into purchasing the book.
Fyi