NotificationsViewModel.cs

public class NotificationsViewModel : AppBaseViewModel
{
	private readonly INotificationService _notificationService;
	private readonly INotificationPresenter _presenter;

	public NotificationsViewModel(INotificationPresenter presenter, INotificationService notificationService)
	{
		_presenter = presenter;
		_notificationService = notificationService;
	}
	
	public override void OnAppearing()
	{
		_notificationService.NotificationsCount.Subscribe((count) =>
            	{
	    		_presenter.UpdateCount();
            	});
	}
}