UIKit

UIKit is a framework developed by Apple Inc. that provides the interfaces needed to construct and manage graphical, event-driven user interfaces for iOS and related platforms. It exposes a comprehensive set of classes for windows, views, controls, navigation, and user interaction, and it coordinates with the system to handle input, layout, and rendering.

Key concepts include UIApplication, UIWindow, UIView, and UIViewController, which form the core of the view hierarchy, as well as UIControls such as UIButton and UISwitch. UIKit also provides container controllers like UINavigationController, UITabBarController, and UIPageViewController, plus table and collection views (UITableView, UICollectionView) for lists and grids.

The framework emphasizes a view-controller architecture, event handling via the responder chain, and layout through Auto Layout with size classes. It integrates with Interface Builder and storyboards, enabling visual interface design and connections to Swift or Objective-C code.

UIKit originated with iOS and expanded to iPadOS and tvOS. With Mac Catalyst, UIKit apps can run on macOS, while watchOS uses WatchKit rather than UIKit for its user interface.

Although SwiftUI has emerged as a modern, declarative alternative, UIKit remains a mature, widely used imperative UI framework. It supports both Swift and Objective-C development and continues to be updated alongside newer Apple platform technologies.