SwiftUI Interface

SwiftUI is Apple's declarative, reactive UI framework for building interfaces on iOS, macOS, tvOS, and watchOS. Instead of imperatively building views (like UIKit), you declare what the UI should be given the current state. SwiftUI automatically updates the UI when state changes. The syntax is clean: views are functions returning View. Modifiers build up the view (styling, layout, behavior). State management is built-in with @State, @ObservedObject, and @EnvironmentObject.