iOS 9 Programming Fundamentals with Swift

Chapter 10. Cocoa Classes

When you program iOS, you’re programming Cocoa. So you need to be acquainted with Cocoa; you have to know, as it were, who you’re talking to when you talk to Cocoa, and what sort of behavior Cocoa is likely to expect from you. Cocoa is a big framework, subdivided into many smaller frameworks, and it takes time and experience to become reasonably familiar with it. Nevertheless, Cocoa has certain chief conventions and primary components that can serve as guideposts from the outset.

The Cocoa API is written mostly in Objective-C, and Cocoa itself consists mostly of Objective-C classes, derived from the root class, NSObject. When programming iOS, you’ll be using mostly the built-in Cocoa classes. Objective-C classes are comparable to and compatible with Swift classes, but the other two Swift object type flavors, structs and enums, are not matched by anything in Objective-C. Structs and enums declared originally in Swift cannot generally be handed across the bridge from Swift to Objective-C and Cocoa. Fortunately, some of the most important native Swift object types are also bridged to Cocoa classes. (See Appendix A for more details about the Objective-C language and how communications work between Swift and Objective-C.)

This chapter introduces Cocoa’s class structure. It discusses how Cocoa is conceptually organized, in terms of its underlying Objective-C features, and then surveys some of the most commonly encountered Cocoa utility classes, concluding with ...