主题：请教

Select Case e.DataCol.Name
    Case "产品","入库","出库"
        Dim dr As DataRow
        Dim mr As DataRow = e.DataRow
        Dim drs As List(of DataRow)
        dr = e.DataTable.Find("[_SortKey] < " & mr("_SortKey") & " And [产品] = '" & mr("产品") & "'", "[_SortKey] Desc")
        If dr Is Nothing Then
            mr("库存") = mr("入库") - mr("出库")
            dr = mr
        End If
        drs = e.DataTable.Select("[_SortKey] >= " & dr("_SortKey") & " And [产品] = '" & dr("产品") & "'", "[_SortKey]")
        For i As Integer = 1 To drs.Count - 1
            drs(i)("库存") = drs(i-1)("库存") + drs(i)("入库") - drs(i)("出库")
        Next
        If e.DataCol.Name = "产品" AndAlso e.OldValue IsNot Nothing AndAlso e.OldValue <> e.NewValue Then
            dr = e.DataTable.Find("[_SortKey] < " & mr("_SortKey") & " And [产品] = '" & e.OldValue & "'", "[_SortKey] Desc")
            If dr Is Nothing Then
                dr = e.DataTable.Find("[产品] = '" & e.OldValue & "'", "[_SortKey]")
                If dr IsNot Nothing Then
                    dr("库存") = dr("入库") - dr("出库")
                End If
            End If
            If dr IsNot Nothing Then
                drs = e.DataTable.Select("[_SortKey] >= " & dr("_SortKey") & " And [产品] = '" & dr("产品") & "'", "[_SortKey]")
                For i As Integer = 1 To drs.Count - 1
                    drs(i)("库存") = drs(i-1)("库存") + drs(i)("入库") - drs(i)("出库")
                Next
            End If
        End If
End Select

请问你要实现的效果是什么,以上代码出现什么错?