这样改一下便可
If e.DataCol.Name = "报备日期" Then
If e.DataRow.IsNull("报备日期") Then
e.DataRow("报备单号") = Nothing
Else
Dim d As Date = e.DataRow("报备日期")
Dim y As Integer = d.Year
Dim m As Integer = d.Month
Dim fd As Date = New Date(y,m,1) '获得该月的第一天
Dim ld As Date = New Date(y+1,m,1) '获得该月的最后一天
Dim bh As String = "B" & Format(d,"yyyyMMdd")
If e.DataRow("报备单号").StartsWith(bh) = False '如果编号的前6位不符
Dim max As String
Dim idx As Integer
max = e.DataTable.Compute("Max(报备单号)","报备日期 >= #" & fd & "# And 报备日期 < #" & ld & "# And [_Identify] <> " & e.DataRow("_Identify")) '取得该月的最大编号
If max > "" Then '如果存在最大编号
idx = CInt(max.Substring(bh.Length,3)) + 1 '获得最大编号的后三位顺序号,并加1
Else
idx = 1 '否则顺序号等于1
End If
e.DataRow("报备单号") = bh & Format(idx,"000")
End If
End If
End If