How to add pins when zooming xamarin forms custom map

I want to add pin to my map when zooming the map, In my map I am highlighting each state in US using pins. When am zooming a state I want to add the pin in that state.How can I do this. I am used this link to develop my map:- https://docs.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/custom-renderer/map/customized-pin

Adding state pin like this

         public void AndroidMap()
            {
            user_loc.IsVisible = false;

        customMap.CustomPins = new List<CustomPin>();

        if (App._listStatesPins.Any())
        {
            foreach (var item in App._listStatesPins)
            {
                var pin = new CustomPin
                {
                    Label = item.state,
                    Position = new Position(item.latitude, item.longitude),
                    StateShortName = item.StateshortName
                };

                pin.Clicked += Pin_Clicked;

                customMap.CustomPins.Add(pin);
                customMap.Pins.Add(pin);
            }
        }

        customMap.MoveToRegion(MapSpan.FromCenterAndRadius(new Position(41.48313, -101.9247649), 
        Xamarin.Forms.Maps.Distance.FromMiles(1200)));
      }

Please Help me