Can you explain what the main application in the iOS system is — UIApplication?

UIApplication is the main class of an application in iOS, which manages the application's lifecycle and interaction with the system.

It is responsible for:

• Handling events such as touches, notifications, and transitions between application states.
• Managing the main run loop of the application.
• Coordinating with other system services.

In a typical application, UIApplication is created automatically and accessible via the singleton shared. Developers usually interact with it through the UIApplicationDelegate delegate, where methods for reacting to launch, background transition, receiving notifications, and other events are implemented.

Example of obtaining a reference to UIApplication:

let app = UIApplication.shared

Thus, UIApplication acts as a link between the iOS system and your application, providing control over its state and events.