private void MyDrawObject_DrawBegin(object sender, EventArgs args)
{
GraphicsLayer graphicsLayerPolygon = MyMap.Layers["PolygonGraphicsLayer"] as GraphicsLayer;
graphicsLayerPolygon.ClearGraphics();
GraphicsLayer graphicsLayerVertices = MyMap.Layers["VerticesGraphicsLayer"] as GraphicsLayer;
graphicsLayerVertices.ClearGraphics();
}