/// <summary>

        /// 总结：用到DocumentManager.Open(filePath)时，如果是ForWrite，就需要用到lock文档锁。

        /// </summary>

        [CommandMethod("T38")]  //测试文档锁

        public void T38()

        {

            //Document doc = Application.DocumentManager.MdiActiveDocument;  //如果是MdiActiveDocument，不需要锁LockDocument。

            Document doc = MyTool.MyTools.OpenDwgFile(@"E:\res\autocad\test.dwg");

            Database db = doc.Database;

            //Database db = new Database();

            //db.ReadDwgFile(@"E:\res\autocad\test.dwg", FileShare.Read, true, null);  //这种方式打开db，不要要锁。

            using(doc.LockDocument())   //这里不锁的话，ForWrite模式打开就会报错，但ForRead模式不报错。但如果是MdiActiveDocument，也不需要锁。

            using (Transaction trans = db.TransactionManager.StartTransaction())

            {

                BlockTable bt = db.BlockTableId.GetObject(OpenMode.ForRead) as BlockTable;

                BlockTableRecord modelSpace = bt[BlockTableRecord.ModelSpace].GetObject(OpenMode.ForWrite) as BlockTableRecord;

                /*

                ObjectId bRefId = ObjectId.Null;

                foreach (ObjectId id in modelSpace)

                {

                    if (id.GetObject(OpenMode.ForRead) is BlockReference)

                    {

                        bRefId = id;

                    }

                    break;

                }

                BlockReference bRef = bRefId.GetObject(OpenMode.ForWrite) as BlockReference;

                bRef.DowngradeOpen();

                 * */

            }

        }