Xamarin.Forms comes with a basic message passing system built in, which is what I assume the author is using. I've used it myself for a client mobile app projec

Xamarin.Forms comes with a basic message passing system built in, which is what I assume the author is using. I've used it myself for a client mobile app project. It makes more sense with an MVVM setup like what Xamarin.Forms and WPF expect for user interfaces, since viewmodels can listen for model state changes that need to be reflected in the UI without requiring loads of explicitly coded delegates/events.