public void Delete(Entity entity)
{
if (entity is Box && Boxes.Contains((Box)entity))
{
Boxes.Remove((Box)entity);
}
if (entity is Polyline && Polylines.Contains((Polyline)entity))
{
Polylines.Remove((Polyline)entity);
}
if (entity is InsertedImage && InsertedImages.Contains((InsertedImage)entity))
{
InsertedImages.Remove((InsertedImage)entity);
}
if (entity is Circle && Circles.Contains((Circle)entity))
{
Circles.Remove((Circle)entity);
}
}