学习老朱例子做库存管理，但出现情况。在没保存的情况下，或修改后撤消修改时，DataColChanging事件不会动作，结果出库数量不准确。请问怎么处理？请大家指教。谢谢。

例子连接http://www.foxtable.com/bbs/dispbbs.asp?BoardID=2&ID=29462&replyID=&skin=1

DataColChanging事件

If e.DataCol.Name = "出库数量" Then
    Dim dr As DataRow = e.DataRow
    Dim pf As String
    pf = e.DataRow("产品名称")
    Dim cmd1 As New SQLCommand
    Dim cmd2 As New SQLCommand
    Dim Key As Integer
    cmd1.C
    cmd2.C
    If pf > "" Then
        cmd1.commandText = "Select [库存数量] From [库存表] Where [产品名称] = \'" & pf & "\'"
        Key = cmd1.ExecuteScalar() \'从后台获得顺序号
        e.DataRow("目前库存数")=key
        If key <= e.NewValue Then
            MessageBox.Show("库存数不够,不能发货!", "提示", MessageBoxButtons.YesNo, MessageBoxIcon.Information)
            e.Cancel =True
        Else
            cmd2.commandText = "Update [库存表] Set [库存数量] = " & (Key - e.NewValue) & " Where [产品名称] = \'" & pf & "\'"
            If cmd2.ExecuteNonQuery() > 0 Then \'更新顺序号
                MessageBox.Show("库存更新成功!", "提示", MessageBoxButtons.YesNo, MessageBoxIcon.Information)
            End If
            Return
        End If
    End If
End If

有人有空帮忙指导下吗？