nav-drawer-add-menu-action-mainactivity.cs

...
    var navigationView = FindViewById<NavigationView>(Resource.Id.nav_view);
    navigationView.NavigationItemSelected += NavigationView_NavigationItemSelected;
}
		void NavigationView_NavigationItemSelected(object sender, NavigationView.NavigationItemSelectedEventArgs e)
		{
			switch (e.MenuItem.ItemId)
			{
				case (Resource.Id.nav_home):
					Toast.MakeText(this, "selecionando menu Home", ToastLength.Short).Show();
					break;
				case (Resource.Id.nav_xamarin):
					Toast.MakeText(this, "selecionando menu Xamarin", ToastLength.Short).Show();
					break;
				case (Resource.Id.nav_microsoft):
					Toast.MakeText(this, "selecionando menu Microsoft", ToastLength.Short).Show();
					break;
				case (Resource.Id.nav_medium):
					Toast.MakeText(this, "selecionando menu Medium", ToastLength.Short).Show();
					break;
				case (Resource.Id.nav_menu1):
					Toast.MakeText(this, "selecionando menu Menu 1", ToastLength.Short).Show();
					break;
				case (Resource.Id.nav_menu2):
					Toast.MakeText(this, "selecionando menu Menu 2", ToastLength.Short).Show();
					break;
				case (Resource.Id.nav_menu3):
					Toast.MakeText(this, "selecionando menu Menu 3", ToastLength.Short).Show();
					break;


			}
		}