Frameworks in Cocoa Programming

By: Aaron Hillegass

A framework is a collection of classes that are intended to be used together. In other words, the classes are compiled together into a reusable library of code. Any related resources are put into a directory with the library. The directory is renamed with the extension .framework. You can find the built-in frameworks for your machine in /System/Library/Frameworks.

Cocoa is made up of three frameworks:

Foundation: Every object-oriented programming language needs the standard value, collection, and utility classes. Strings, dates, lists, threads, and timers are in the Foundation framework.
AppKit: All things related to the user interface are in the AppKit framework. Windows, buttons, text fields, events, and drawing classes are in the AppKit. You will also see this framework called the ApplicationKit.
Core Data: Core Data makes it easy to save your objects to a file and then reload them into memory. We say that Core Data is a persistence framework.

Numerous other frameworks handle such duties as encryption, QuickTime, and CD burning. Foundation, AppKit, and Core Data are the most commonly used. Once you have mastered these, the other frameworks will be easier to understand.

You can also create your own frameworks from the classes that you create. Typically, if a set of classes is used in several applications, you will want to turn them into a framework.