[讨论]如何保存及读取dwg文件啊

/// 
    /// 保存dwg文件
    /// 
    /// 要保存的实体
    public void AddEntity(Entity entity)
    {
      Document doc = AcadApp.DocumentManager.MdiActiveDocument;
      Database db = doc.Database;
      using (Transaction trans = db.TransactionManager.StartTransaction()) {
        BlockTable bt = (trans.GetObject(db.BlockTableId, OpenMode.ForWrite)) as BlockTable;
        BlockTableRecord btr = (trans.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite)) as BlockTableRecord;
      
        ObjectId objectId = btr.AppendEntity(entity);
        trans.AddNewlyCreatedDBObject(entity, true);
        trans.Commit();
        trans.Dispose();
      }
      db.SaveAs(@"../../../../test.DWG", DwgVersion.Current);
    }
[CommandMethod("AddArc")]
    public void AddArc()
    {
      Arc arc = new Arc(new Point3d(100, 200, 300), 50, 60, 30);
      AddEntity(arc);
    }