主题：代码修改

当同时删除多行时,出错:

 

错误代码位置：表，货品资料，BeforeDeleteDataRow

System.NullReferenceException: 未将对象引用设置到对象的实例。
   在 UserCode.BeforeDeleteDataRow(DataRowEventArgs e)

 

 

请问下面代码如何修改?

 

Dim d1 As String = CurrentTable.Current("一级类别") '

Dim d2 As String = CurrentTable.Current("二级类别")
Dim d3 As String = CurrentTable.Current("三级类别")
Dim d4 As String = CurrentTable.Current("四级类别")
Dim d5 As String = CurrentTable.Current("五级类别")
Dim d6 As String = CurrentTable.Current("六级类别")
Dim dr1 As List(of DataRow) = e.DataTable.Select("一级类别 Like '" & d1 & "'") '

Dim dr2 As List(of DataRow) = e.DataTable.Select("一级类别 Like '" & d1 & "'And 二级类别 Like '" & d2 & "'")
Dim dr3 As List(of DataRow) = e.DataTable.Select("一级类别 Like '" & d1 & "'And 二级类别 Like '" & d2 & "'And 三级类别 Like '" & d3 & "'")
Dim dr4 As List(of DataRow) = e.DataTable.Select("一级类别 Like '" & d1 & "'And 二级类别 Like '" & d2 & "'And 三级类别 Like '" & d3 & "'And 四级类别 Like '" & d4 & "'")
Dim dr5 As List(of DataRow) = e.DataTable.Select("一级类别 Like '" & d1 & "'And 二级类别 Like '" & d2 & "'And 三级类别 Like '" & d3 & "'And 四级类别 Like '" & d4 & "'And 五级类别 Like '" & d5 & "'")
Dim dr6 As List(of DataRow) = e.DataTable.Select("一级类别 Like '" & d1 & "'And 二级类别 Like '" & d2 & "'And 三级类别 Like '" & d3 & "'And 四级类别 Like '" & d4 & "'And 五级类别 Like '" & d5 & "'And 六级类别 Like '" & d6 & "'")
Dim d7 As String = "该行包含类别, 是否删除?"
If (dr6 IsNot Nothing And dr6.count = 1) OrElse (dr5 IsNot Nothing And dr5.count = 1) OrElse (dr4 IsNot Nothing And dr4.count = 1) OrElse (dr3 IsNot Nothing And dr3.count = 1) OrElse (dr2 IsNot Nothing And dr2.count = 1) OrElse (dr1 IsNot Nothing And dr1.count = 1) Then
If MessageBox.Show(d7,"提示",MessageBoxButtons.YesNo,MessageBoxIcon.Question) = DialogResult.No Then
        e.Cancel= True
Else

End If
End If

谢谢!