主题：录入凭证设计

红色标注的代码报错：

Dim yzdh As WinForm.TextBox = e.Form.Controls("dh")'dh是单号控件

Dim di As String = yzdh.Value 'di单号控件中的变量

Dim bsrq As WinForm.DateTimePicker = Forms("月租收费").Controls("rq")

Dim d As Date = bsrq.Value

If d = "" Then

    messagebox.show("请选择日期")

    Return

Else

    Dim y As Integer = d.Year

    Dim m As Integer = d.Month

    Dim Days As Integer = Date.DaysInMonth(y,m)

    Dim fd As Date = New Date(y,m,1) '获得该月的第一天

    Dim ld As Date = New Date(y,m,Days) '获得该月的最后一天

    'Dim bh As String = DataTables("缴费情况").DataRow("前缀") & "-" & Format(d,"yyyyMM") & "-" '生成编号的前缀

    Dim bh As String = "yz" & "-" & Format(d,"yyyyMM") & "-" '生成编号的前缀

        Dim max As String

        Dim idx As Integer

        Dim flt As String

        flt = "[前缀] = 'yz'" & " And [日期] >= #" & fd & "# And [日期] <= #" & ld & "# And [_Identify] <> " & DataTables("缴费情况").DataRow("_Identify")

        'flt = "[前缀] = '" & DataTables("缴费情况").DataRow("前缀") & "' And [日期] >= #" & fd & "# And [日期] <= #" & ld & "# And [_Identify] <> " & DataTables("缴费情况").DataRow("_Identify")

        max = DataTables("缴费情况").Compute("Max(单号)",flt) '取得该月的相同工程代码的最大单据编号

        If max > "" Then '如果存在最大单据编号

            idx = CInt(max.Substring(10,4)) + 1 '获得最大单据编号的后四位顺序号,并加1

        Else

            idx = 1 '否则顺序号等于1

        End If

        di = bh & Format(idx,"0000")

    End If

End If