Bind-able layer for Bing Maps

I had a special requirement on showing items on Bing Map.

I needed to show a collection of collections of objects - in this case bike routes. Actually each route was composed of collection of routes (which could be interconnected at some places).

This cannot be achieved only by MapItemsControl - which can render only one dimensional collection.

So what I really need was to add dynamically a collection of MapItemsControl to the map.

Instead of using MapItemsControl I have decided to use the MapLayer class. I have created a new layer, which exposes a DependencyProperty "Routes".

This property can be bound to a two dimensional collection. I use List of Lists, but I guess I should have used IEnumerable to make the usage more general. When the collection changes, the routes are drawn to the card, by creating MapPolyline objects.

Of course a similar class could be created for Pushpins - and for displaying a set of set's of places.

When taken further, actually this approach could even expose a Template which could be set to specify how each item of the group will be rendered.

Here is the code:

public class BikeRoutesLayer : MapLayer
{
    private static Color[] _colors = { Colors.Blue, Colors.Green, Colors.Orange,Colors.Gray };

    public List<List<LocationCollection>> Routes
    {
        get { return (List<List<LocationCollection>>)GetValue(RoutesProperty); }
        set { SetValue(RoutesProperty, value); }
    }
    public static readonly DependencyProperty RoutesProperty =
        DependencyProperty.Register("Routes", typeof(List<List<LocationCollection>>), typeof(BikeRoutesLayer), new PropertyMetadata(new PropertyChangedCallback(RoutesChangedCallBack)));
    
    static int i = 0;
    private static void RoutesChangedCallBack(DependencyObject sender, DependencyPropertyChangedEventArgs args)
    {
        var layer = sender as BikeRoutesLayer;

        var list = args.NewValue as List<List<LocationCollection>>;

        if (list != null)
        {
            foreach (var bikeRoute in list)
            {
                foreach (var route in bikeRoute)
                {   
                    MapPolyline line = new MapPolyline();
                    line.Locations = route;
                    line.StrokeThickness = 1;
                    line.Stroke = new SolidColorBrush(_colors[i%_colors.Length]);
                    layer.Children.Add(line);
                }
                i++;
            }
        }
    }
}