调试Autodesk官方例题出现的问题

heidong2002

        [CommandMethod("createLayer")]
        public ObjectId CreateLayer()   //-----------------------------------1-------------------------------
        {
            ObjectId layerId=new ObjectId(); //它返回函数的值
            Database db = HostApplicationServices.WorkingDatabase;
            Editor ed = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.Editor;
            Transaction trans = db.TransactionManager.StartTransaction();
            //首先取得层表……
            LayerTable lt = (LayerTable)trans.GetObject(db.LayerTableId, OpenMode.ForWrite);
            //检查EmployeeLayer层是否存在……
            if (lt.Has("EmployeeLayer"))
            {
                layerId = lt["EmployeeLayer"];
            }
            else
            {
                //如果EmployeeLayer层不存在，就创建它
                LayerTableRecord ltr = new LayerTableRecord();
                ltr.Name = "EmployeeLayer"; //设置层的名字
                ltr.Color = Color.FromColorIndex(ColorMethod.ByAci, 2);
                layerId = lt.Add(ltr);
                trans.AddNewlyCreatedDBObject(ltr, true);
            }
            trans.Commit();

            trans.Dispose();
            return layerId; //-----------------------------------2-------------------------------
        }

调试时报错，但将程序返回类型改为void：-----1--------处改为public void CreateLayer()   ，-------2------处去掉，则可正常建立层，这是为什么？

另外，要将建立的层设为当前层，我该怎么做？