以下代码是在Datacolchanged事件中执行的。是哪里错了？为何总是总得不到库存不足的提示呢？

Dim po As String = e.DataRow("PO")
Dim ty As String = e.DataRow("material_type")
Dim name As String = e.DataRow("material_name")
Dim size As String = e.DataRow("material_size")
Dim color As String = e.DataRow("color")
Dim pdr As DataRow = DataTables("库存表").Find("PO = \'" & po & "\' And material_type = \'" & ty & "\' And material_name = \'" & name & "\' And material_size = \'" & size & "\' And material_color = \'" & color & "\'")

If e.DataCol.name = "quantity"  And pdr Is Nothing Then

End If

这样看看

If e.DataCol.name = "quantity"
Dim po As String = e.DataRow("PO")
Dim ty As String = e.DataRow("material_type")
Dim name As String = e.DataRow("material_name")
Dim size As String = e.DataRow("material_size")
Dim color As String = e.DataRow("color")
Dim pdr As DataRow = DataTables("库存表").Find("PO = \'" & po & "\' And material_type = \'" & ty & "\' And material_name = \'" & name & "\' And material_size = \'" & size & "\' And material_color = \'" & color & "\'")
if pdr Isnot Nothing Then
If pdr("stocking_qty") < e.NewValue  Then
MessageBox.Show("库存不足")
End If
else
MessageBox.Show("没有符合条件的数据")
End If

此主题相关图片如下：库存表结构.jpg

谢谢你的答复，不过还是得不到提示；我的出库表和库存表有关联和表达式；是否会对此有影响？我将条件改为

pdr("stocking_qty") < 0   也不行。怎么回事呀？