How do I run a macro on change to a field, but not on original entry of that field? - vba

Question

I created a Projects database which includes a form with fields for staff to complete on startup of a project.
The first field, 'ClientCode' is a compulsory dropdown list (Combobox) of Clients.
To avoid accidental changes to this field, I added 'On Change' code to display a warning message:
Private Sub ComboClientCode_Change()
If MsgBox("Are you sure you want to change the client?", vbQuestion + vbYesNo) = vbNo Then
DoCmd.RunCommand acCmdUndo
Else
Exit Sub
End If
End Sub
It works, however I don't want it to run when someone starts a new record i.e. selects the client for the first time.
How do I make this message only show if it is a change to the original entry?
I tried moving it to 'AfterUpdate' but it does the same thing.

Answer 1

Right, I haven't tested any of the code below so let me know if it works for you. I propose 2 different solutions, and depending on if the logic works, the solution will work.
Solution 1:
Using the change event, you check the combobox value, and if it is blank then run the code. My concern with this is that when the event handler fires there will only be a value in there because the user would have changed the value to call the event handler. Nonetheless, the code would look like something below.
Private Sub ComboClientCode_Change()
If Me.ComboClientCode.Value <> "" Then
If MsgBox("Are you sure you want to change the client?", vbQuestion + vbYesNo) = vbNo Then
DoCmd.RunCommand acCmdUndo
Else
Exit Sub
End If
End If
End Sub
Solution 2:
With this solution the logic seems a bit more sound than the above method. What will happen is you will set the default value of the combobox using the UserForm_Initialize() event handler. Then, when your user selects from the dropdown list it will set the value to that variable, and will prevent the unnecessary pop up. See below code. Your userform module should look like the below.
Option Explicit
Dim sClientCode As String
Private Sub UserForm_Initialize()
sClientCode = Me.ComboClientCode.Value
End Sub
Private Sub ComboClientCode_Change()
If sClientCode <> "" Then
If MsgBox("Are you sure you want to change the client?", vbQuestion + vbYesNo) = vbNo Then
'set the value now
sClientCode = Me.ComboClientCode.Value
DoCmd.RunCommand acCmdUndo
Else
Exit Sub
End If
End If
End Sub

Answer 2

You could change one of the "irrelevant" properties of the combobox the first time it gets changed.
Private Sub ComboClientCode_Change()
If ComboClientCode.ColumnHeads = False Then
ComboClientCode.ColumnHeads = True
Else
If MsgBox("Are you sure you want to change the client?", vbQuestion + vbYesNo) = vbNo Then
'DoCmd.RunCommand acCmdUndo
Debug.Print "DoCmd.RunCommand acCmdUndo"
Else
Exit Sub
End If
End If
End Sub
Should work for this type:
Listed properties of above selected type:
You can run this to make the existing one change if it has a value:
Sub Switch()
If ComboClientCode.Value <> "" Then
ComboClientCode.ColumnHeads = True
Else
ComboClientCode.ColumnHeads = False
End If
End Sub