What is the role and functions of the AppDelegate class in an iOS application?

AppDelegate in an iOS application is responsible for the application's lifecycle and handling system events. This class receives notifications about launch, entering background, activation, termination, and other application states. In AppDelegate, initial parameters are usually configured, services are initialized, and incoming notifications and URL schemes are processed.

Example methods of AppDelegate:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // Application initialization
    return true
}

func applicationDidEnterBackground(_ application: UIApplication) {
    // Saving state when entering background
}