Objective-C is fairly simple, while Cocoa is vast and complex. The distinct is important.
It might take you awhile to get familiar with Cocoa and all its patterns built on top of NSObject.
"Cocoa Design Patterns, by Buck and Yacktman" is a very good book to get the big picture right, but might be slightly overwhelming at the beginning (as there are many patterns/ways to solve the same problem in Cocoa).
Read Apple's documents: I still find it the best way to learn the details of Cocoa. The writing is dry and quite dense, so you might need to read it multiple times.
Another thing to remember is that Cocoa is a framework: it demands to be followed and not be fought against.
It might take you awhile to get familiar with Cocoa and all its patterns built on top of NSObject.
"Cocoa Design Patterns, by Buck and Yacktman" is a very good book to get the big picture right, but might be slightly overwhelming at the beginning (as there are many patterns/ways to solve the same problem in Cocoa).
Read Apple's documents: I still find it the best way to learn the details of Cocoa. The writing is dry and quite dense, so you might need to read it multiple times.
Another thing to remember is that Cocoa is a framework: it demands to be followed and not be fought against.