UDF - Identify if it's a recalculation or first execution - excel

Question

I want to program a UDF to query a access db. I'm wondering if it's possible to have 2 different Workflows, depending whether it's a first execution or only a recalculation of the UDF.
Ideally I would have a UDF that you can feed the primary key of the db and the UDF presents an overview of possible values of the access db table. If it's a recalculation I don't want to have a userform popup again. Is this possible at all? Can somebody point me in the right direction?
Thx!
Edit
An attempt to show some (dummy) code:
public function key_from_table(primarykey as string) as string
' Read-out column names from Access table for userform
' Trigger userform with possible column names and let user choose
' readout Chosen column names
key_from_table = Call get_from_db(Primary_key, column_names)
end function
Function get_from_db(Primarykey as string, column_names as string) as string
'call Access db and readout result
end Function
If a recalculation is triggered the userform popup comes up again
I'm still new to Excel vba - pls tell me if this is rather stupid :)

Answer 1

Declares a global dictionary variable. Just before you trigger the form, check if dictionary already has the column name. If it does, don't trigger the form. If it doesn't, trigger the form and add the column name to dictionary once form is closed. You can clear the variable in Workbook_BeforeClose just to be clean

Answer 2

Something like this should work for you:
Public pub_sRecalcCheck As String
Public Function MyTest() As Boolean
Dim bReCalc As Boolean
If InStr(1, " " & pub_sRecalcCheck & " ", " " & Application.Caller.Address(External:=True) & " ", vbTextCompare) = 0 Then
'This is a brand new calculation
'Add this cell to the public variable storing where calculations for this UDF have occurred
bReCalc = False
pub_sRecalcCheck = WorksheetFunction.Trim(Replace(pub_sRecalcCheck, " " & rCell.Address(External:=True) & " ", " "))
''''''''''''''''''''''''''''''''''''''''''''
' '
' Your code here for new calculation '
' '
''''''''''''''''''''''''''''''''''''''''''''
Else
'This is a recalculation
bReCalc = True
''''''''''''''''''''''''''''''''''''''''''
' '
' Your code here for recalcuations '
' '
''''''''''''''''''''''''''''''''''''''''''
End If
MyTest = bReCalc
End Function
EDIT: And just in case the formula gets deleted from the cell, use this in the ThisWorkbook module to clear that cell's address from the RecalcCheck public string variable so that if a new formula is put there it is treated as a new calculation:
Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
Dim rCell As Range
For Each rCell In Target.Cells
'Check if cell has been deleted/cleared
If IsEmpty(rCell) Then
'Found deleted cell, check if it is stored for the recalc checks
If InStr(1, " " & pub_sRecalcCheck & " ", " " & rCell.Address(External:=True) & " ", vbTextCompare) > 0 Then
'It is stored, remove it so that if formula is put back it is treated as a new calculation
pub_sRecalcCheck = WorksheetFunction.Trim(Replace(pub_sRecalcCheck, " " & rCell.Address(External:=True) & " ", " "))
End If
End If
Next rCell
End Sub