UIKit is a graphical, event-driven framework for building apps on Apple platforms.
Features
Has extensive API coverage — Provides an extensive library of items in its framework, including the core objects, views, and controls that you’ll need to build native apps with little or no modifications.
Includes Interface Builder — You can visually design complex views and their relationships. With Interface Builder and Auto Layout, you can ensure your UI looks and works great across all devices and orientations.
Supports a rich legacy — Before iOS 13, developers built all apps on UIKit. If you’re maintaining or extending legacy apps on iOS, watchOS, or tvOS, you’ll need a good foundation in UIKit.
Has strong community adoption — You can access numerous UIKit articles and community support options.
Is interoperable with SwiftUI — You can easily integrate UIKit and SwiftUI and use the best of both frameworks.