Many of the best resources on Cocoa development are installed on your hard drive when you install Apple’s Developer Tools. These documents, mirrored online (http://developer.apple.com/techpubs), include but aren’t limited to the following:
Updated with every release of Mac OS X, these notes are typically one step ahead of the rest of Apple’s documentation. You should read through these every time you update your system so that you can stay on top of the latest changes to the system.
This is the definitive reference for the Objective-C programming language, and is a must-read for all Cocoa developers. HTML and PDF versions of this document can be found on the Cocoa Documentation web site and on your system.
This is a two-volume set, published by Apple through Vervanté, contains the complete reference documentation for the Foundation framework. This is the same material found online at Apple’s Cocoa documentation web site, and on your hard drive as part of the developer tools installation.
Like the Foundation Reference for Objective-C, this book is a three-volume set that contains the complete reference documentation for the Application Kit framework.