about field update using function with case - ms-access

Question

I'm trying to update some field value depending two string field using a function with If and Case, function below:
Private Function checkDATI(tipotransazione As String, tipovendita As String) As String
Dim r As String
r = ""
If tipotransazione = "VENDITA" Then
Select Case tipovendita
Case "ARMI"
If Me.txtMatricola = "" Then r = "Matricola"
If Me.txtModello = "" Then r = "Modello"
If Me.txtCalibro = "" Then r = "Calibro"
If Me.txtTipoArma = "" Then r = "Tipo Arma"
If Me.txtFabrica = "" Then r = "Fabbrica"
Case "VENDITA ARMI/MUNIZIONI"
Case "MUNIZIONI"
End Select
End If
If tipotransazione = "ACQUISTO" Then
Select Case tipovendita
Case "ARMI"
If Me.txtMatricola = "" Then r = "Matricola"
If Me.txtModello = "" Then r = "Modello"
If Me.txtCalibro = "" Then r = "Calibro"
If Me.txtTipoArma = "" Then r = "Tipo Arma"
If Me.txtFabrica = "" Then r = "Fabbrica"
Case "VENDITA ARMI/MUNIZIONI"
Case "MUNIZIONI"
End Select
End If
checkDATI = r
End Function
And then when I call this function in a command button event as:
MsgBox (checkDATI(Me.CausaleMov, Me.txt_tipomov))
It's not updating that field. What is wrong?

Answer 1

When you say:
If Me.txtMatricola = "" Then r = "Matricola"
What you are doing is assigning the value: "Matricola" to the variable:r. Instead what I think you want is this:
If Me.txtMatricola = "" Then Me.txtMatricola = "Matricola"
This actually sets the value of the field: txtMatricola to "Matricola". This goes for all of the fields that are in your Case statements.