Basics of Cocoa Touch in iOS Apps
The Cocoa Touch layer contains most of the object-oriented developer-facing frameworks for building iOS applications. It is your single point of entry to app development. The Apple guides encourage you to investigate the technologies in this layer to see whether they meet your needs, before looking at the other layers.
In other words, Apple intends for Cocoa Touch to be your single point of entry into iOS app development. The Cocoa Touch framework and the Foundation framework make up the two key iOS development components used by developers. Use all the other components on an as-needed basis.
Cocoa Touch is where you build your app’s user interface, handle touch-based and gesture-based interactions, connect the user interface to the app’s data, deal with multitasking, and integrate everything from state preservation to push notification to printing.
Cocoa Touch provides object-oriented access for managing your address book and events, building games, and dealing with ads, maps, messages, social media, and sensors. Most of the time, you should work through Cocoa Touch; because it provides seemless access to the other layers of the technology. In particular, you will work with the UIKit framework, which packages most of the functionality just described.
The Cocoa Touch framework and the Foundation framework make up the two key iOS development components used by developers. Use all the other components on an as-needed basis. At times, you may need direct access to the lower layers.