namespace CircleViewerMac { [Register("AppDelegate")] public class AppDelegate : UIApplicationDelegate { public override UIWindow? Window { get; set; } public override bool FinishedLaunching(UIApplication application, NSDictionary launchOptions) { // create a new window instance based on the screen size Window = new UIWindow(UIScreen.MainScreen.Bounds); // create a UIViewController with a single UILabel var vc = new UIViewController(); vc.View!.AddSubview(new UILabel(Window!.Frame) { BackgroundColor = UIColor.SystemBackground, TextAlignment = UITextAlignment.Center, Text = "Hello, Mac Catalyst!", AutoresizingMask = UIViewAutoresizing.All, }); Window.RootViewController = vc; // make the window visible Window.MakeKeyAndVisible(); return true; } } }