ms-access - 无效使用 null Access-VBA

Question

我在使用这个按钮时遇到错误，因为如果，给出错误无效使用 null，有人可以解释一下吗？

Sub Concluído_Click()

    Dim novonome As String
    Dim dataadmi As Date
    Dim datanasc As Date
    Dim Email As Hyperlink
    Dim Cargo As String
    Dim Categoria As String
    Dim ingless As String
    Dim inglesw As String
    Dim coordeq As String
    Dim relcli As String
    Dim Java As String
    Dim SQL As String
    Dim PHP As String
    Dim wserv As String
    Dim Vendas As String
    Dim dgraf As String
    Set table = New ADODB.Recordset

    With Form_Funcionários


**If Len(.Nome.value & "") = 0 Or _
    ValornaColuna(.Nome.value, "Funcionários", "Nome") = True Then**
            MsgBox "Campo Nome do Formulario encontra-se vazio ou ja existe! Por favor altere o seu valor!", vbOKOnly, "Campo Vazio"
        End If
    End With


    HideAll

End Sub

Private Function ValornaColuna(ByVal value As String, ByVal formTable As String, ByVal formColumn As String) As Boolean

    Dim valueToCompare As String
    Dim C As Boolean
    Set table = New ADODB.Recordset

    table.Open formTable, CurrentProject.Connection, adOpenDynamic, adLockReadOnly
    C = False

    While table.EOF = False And ExistsInColumn = False
        valueToCompare = table.Fields(formColumn)

        If StrComp(valueToCompare, value, vbTextCompare) = 0 Then
            C = True
        End If
        table.MoveNext
    Wend

    table.Close
End Function

Answer 1

每当 .Nome.value 时，这都会抛出错误(无效使用 Null)为空，因为 ValornaColuna需要 String 作为其第一个参数的数据类型。而且 Null 不是 String 类型。

If Len(.Nome.value & "") = 0 Or _
    ValornaColuna(.Nome.value, "Funcionários", "Nome") = True Then

您可以通过使用 Nz 来避免该错误。每当 .Nome.value 时传入一个空字符串为空。

If Len(.Nome.value & "") = 0 Or _
    ValornaColuna(Nz(.Nome.value, vbNullSting), "Funcionários", "Nome") = True Then