iOSHighlightableMapRenderer.cs

[assembly: ExportRenderer(typeof(HighlightableMap), typeof(IosHighlightableMapRenderer))]

public class IosHighlightableMapRenderer : MapRenderer
{
    private MapHighlight _currentHighlight;

    protected override void OnElementChanged(ElementChangedEventArgs<View> e)
    {
        base.OnElementChanged(e);

        if (e.OldElement != null)
        {
            if (Control is MKMapView nativeMap)
            {
                nativeMap.RemoveOverlays(nativeMap.Overlays);
                nativeMap.OverlayRenderer = null;
            }
        }

        if (e.NewElement != null)
        {
            if (Control is MKMapView nativeMap)
            {
                nativeMap.OverlayRenderer = OverlayRendererHandler;
                OnUpdateHighlight();
            }
        }
    }

    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);
        if (e.PropertyName == nameof(HighlightableMap.Highlight))
        {
            OnUpdateHighlight();
        }
    }

    private void OnUpdateHighlight()
    {
        var highlightableMap = (HighlightableMap)Element;
        var nativeMap = Control as MKMapView;
        if (highlightableMap == null || nativeMap == null) return;

        nativeMap.RemoveOverlays(nativeMap.Overlays);

        if (highlightableMap?.Highlight == null) return;

        _currentHighlight = highlightableMap.Highlight;

        var overlays = new List<IMKOverlay>();
        foreach (var polygon in highlightableMap.Highlight.Polygons)
        {
            var coordinates = new List<CLLocationCoordinate2D>();
            foreach (var position in polygon.Positions)
            {
                coordinates.Add(new CLLocationCoordinate2D(position.Latitude, position.Longitude));
            }

            var blockOverlay = MKPolygon.FromCoordinates(coordinates.ToArray());
            overlays.Add(blockOverlay);
        }

        nativeMap.AddOverlays(overlays.ToArray());
    }

    private MKOverlayRenderer OverlayRendererHandler(MKMapView mapView, IMKOverlay overlayWrapper)
    {
        if (_currentHighlight != null)
        {
            var overlay = Runtime.GetNSObject(overlayWrapper.Handle) as IMKOverlay;
            return new MKPolygonRenderer(overlay as MKPolygon)
            {
                FillColor = _currentHighlight.FillColor.ToUIColor(),
                StrokeColor = _currentHighlight.StrokeColor.ToUIColor(),
                LineWidth = (nfloat)_currentHighlight.StrokeThickness
            };
        }
        return null;
    }
}