c#，获取cad中直线的图层

vs2010下，获取CAD选中直线的图层
有人了解吗？谢谢帮忙！

[CommandMethod("GLL")]
        public void GetLineLayer()
        {
            var ed = Application.DocumentManager.MdiActiveDocument.Editor;
            PromptEntityOptions pEntOpts = new PromptEntityOptions("请选取直线:");
            pEntOpts.AddAllowedClass(typeof(Line), true);
            PromptEntityResult pEntRes = ed.GetEntity(pEntOpts);
            if (pEntRes.Status != PromptStatus.OK)
                return;
            ed.WriteMessage(
                $"\n直线所在图层为{(pEntRes.ObjectId.GetObject(OpenMode.ForRead) as Line)?.Layer}");
        }