UIKit (not to be confused with the front-end framework getuikit) is the object-oriented framework that is responsible for most of the ios user interface. UIKit is part of the cocoa-touch umbrella framework, and it is to Cocoa Touch as AppKit is to the Cocoa framework on macOS. The classes in UIKit determine the basic structure of most iOS applications as well as the majority of distinctive user interface elements that make iOS apps easily recognizable and instantly familiar.
UIKit provides the classes and protocols that lie at the foundation of any iOS application, including:
It also provides the user interface elements with which all iOS users are familiar:
These lists are not exhaustive, but only meant to give a sense of the scope of the UIKit framework. A more complete list is found in the UIKit Framework Reference.