已解决-ShowModalDialog一个FORM，单击按钮画圆，提交事务却没画上，怎么回事儿？

private void OKButton_Click(object sender, EventArgs e)//确定按钮
    {
      // 获得当前文档和数据库   Get the current document and database
      Document acDoc = AcadApp.DocumentManager.MdiActiveDocument;
      Database acCurDb = acDoc.Database;
      // 启动一个事务  Start a transaction
      using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
      {
        // 以只读方式打开块表   Open the Block table for read
        BlockTable acBlkTbl;
        acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId,
                                     OpenMode.ForRead) as BlockTable;
        // 以写方式打开模型空间块表记录   Open the Block table record Model space for write
        BlockTableRecord acBlkTblRec;
        acBlkTblRec = acTrans.GetObject(acBlkTbl[BlockTableRecord.ModelSpace],
                                        OpenMode.ForWrite) as BlockTableRecord;
        // 创建一个中心点在 (2,3,0) ，半径为4.25 的圆  Create a circle that is at 2,3 with a radius of 4.25
        Circle acCirc = new Circle();
        acCirc.SetDatabaseDefaults();
        acCirc.Center = new Point3d(2, 3, 0);
        acCirc.Radius = 4.25;
        // 添加新对象到块表记录和事务中   Add the new object to the block table record and the transaction
        acBlkTblRec.AppendEntity(acCirc);
        acTrans.AddNewlyCreatedDBObject(acCirc, true);
        // 保存新对象到数据库中   Save the new object to the database
        acTrans.Commit();
      }
    }