Why the cell values of virtual grid cannot be changed as like normal grid in WinForms GridControl?

// Trigger the required events
this.gridControl1.QueryCellInfo += new GridQueryCellInfoEventHandler(GridQueryCellInfo);
this.gridControl1.SaveCellInfo += new GridSaveCellInfoEventHandler(GridSaveCellInfo);
this.gridControl1.Model.QueryRowCount += gridControl1_QueryRowCount;
 
private void gridControl1_QueryRowCount(object sender, GridRowColCountEventArgs e)
{
   e.Count = this._extData.RowCount;
   e.Handled = true;
}
 
//Saves the changes back to the datasource
private void GridSaveCellInfo(object sender, GridSaveCellInfoEventArgs e)
{
   try
   {
      //Move the changes back to the external data object
      if (e.ColIndex > 0 && e.RowIndex > 0)
   {
      //Either of the next two lines will work without setting CellValueType
      this._extData(e.RowIndex - 1, e.ColIndex - 1) = int.Parse(e.Style.CellValue.ToString());
   }
   }
   catch
   {
   }
   e.Handled = true;
}
 
private void GridQueryCellInfo(object sender, GridQueryCellInfoEventArgs e)
{
   //Sets the cell value from ExternaData
   if (e.RowIndex > 0 && e.ColIndex > 0)
   {
   e.Style.CellValue = this._extData(e.RowIndex - 1, e.ColIndex - 1);
   e.Handled = true;
   }
      //Cell values should be accessed only in events for virtual grid.
      if (e.RowIndex == 0 && e.ColIndex == 11)
   {
     object test3 = "Sep";
     object colname = e.Style;
     colname.Text = test3;
     e.Style.Text = colname.Text;
   }
}

'Trigger the required events
AddHandler gridControl1.QueryCellInfo, AddressOf GridQueryCellInfo
AddHandler gridControl1.SaveCellInfo, AddressOf GridSaveCellInfo
Me.gridControl1.Model.QueryRowCount += gridControl1_QueryRowCount
 
Private Sub gridControl1_QueryRowCount(ByVal sender As Object, ByVal e As GridRowColCountEventArgs)
   e.Count = Me._extData.RowCount
   e.Handled = True
End Sub
 
'Saves the changes back to the datasource
Private Sub GridSaveCellInfo(ByVal sender As Object, ByVal e As GridSaveCellInfoEventArgs)
   Try
   'Move the changes back to the external data object
   If e.ColIndex > 0 AndAlso e.RowIndex > 0 Then
   'Either of the next two lines will work without setting CellValueType
   Me._extData(e.RowIndex - 1, e.ColIndex - 1) = Integer.Parse(e.Style.CellValue.ToString())
   End If
   Catch
   End Try
   e.Handled = True
End Sub
 
 
Private Sub GridQueryCellInfo(ByVal sender As Object, ByVal e As GridQueryCellInfoEventArgs)
   'Sets the cell value from ExternaData
   If e.RowIndex > 0 AndAlso e.ColIndex > 0 Then
   e.Style.CellValue = Me._extData(e.RowIndex - 1, e.ColIndex - 1)
   e.Handled = True
   End If
   'Cell values should be accessed only in events for virtual grid.
   If e.RowIndex = 0 AndAlso e.ColIndex = 11 Then
   Dim test3 = "Sep"
   Dim colname = e.Style
   colname.Text = test3
   e.Style.Text = colname.Text
   End If
End Sub