cad.net 图层隐藏 IsHidden 用法 eDuplicateRecordName 报错

    public class Command_hbtcWin22222
    {
        [CommandMethod("Hiddenlayer")]
        public void Hiddenlayer()
        {
            Document doc = Application.DocumentManager.MdiActiveDocument;
            Database db = doc.Database;
            Editor ed = doc.Editor;

            using (Application.DocumentManager.MdiActiveDocument.LockDocument())//锁文档
            {
                using (Transaction tr = db.TransactionManager.StartTransaction())
                {
                    LayerTable table = tr.GetObject(db.LayerTableId, OpenMode.ForWrite) as LayerTable;

                    string ss = "Test"; 
                    LayerTableRecord layerName = null;
                    if (table.Has(ss))
                    {
                        foreach (var item in table)
                        {
                            layerName = tr.GetObject(item, OpenMode.ForRead) as LayerTableRecord;
                            if (layerName.Name == ss)
                            {
                                layerName.UpgradeOpen();
                                layerName.IsHidden = true;
                                layerName.DowngradeOpen();
                                break;
                            }
                        } 
                    }
                    else
                    {
                        layerName = new LayerTableRecord
                        {
                            Name = ss,
                            IsHidden = false
                        };
                        table.Add(layerName);
                        tr.AddNewlyCreatedDBObject(layerName, true);
                    }
                    table.DowngradeOpen();
                    table.Dispose();
                    tr.Commit();
                }
            }
        }
    }