主题：[求助]保存之前判断空值

我的代码放到了全局项目事件beforesavedatarow里，意思是保存之前先检查是否有空值，但不起作用。代码如下：

With CurrentTable
    For i As Integer = .TopPosition To .BottomPosition
        Dim r As Row = .Rows(i)
        Dim cls() As String
        Select Case .DataTable.name
            Case "Dwxx"
                cls = New String(){"单位全称","单位简称"}
            Case "Xcgl_jjd"
                cls = New String(){"发放时间"}
            Case "Xcgl_jjpf"
                cls = New String(){"奖金名称","奖金类别","批复时间","批复金额"}
            Case "Xcgl_kqtjb"
                cls = New String(){"本月应出勤"}
            Case "Xcgl_工资单"
                cls = New String(){"身份证号"}
            Case "员工信息表"
                cls = New String(){"姓名","身份证号","员工类别"}               
        End Select
        For Each c As String In cls
            If r.isnull(c) Then
                MessageBox.Show("[" & c & "]列不能为空!","提示",MessageBoxButtons.ok,MessageBoxIcon.warning)
                'msgbox("[" & c & "]列不能为空!")
                Return
            End If
        Next
    Next
End With