Can I use VBA function to return a (dynamic) list of acceptable values into Excel's data validation?

Question

For a given cell, I select Data/Validation and set Allow to \"List\". I now wish to set Source like so:

=rNames(REGS)

but that does not work (name not found

Answer 1

I think the problem is that data validation dialog only accepts the following "lists":

• an actual list of things entered directly into the Source field

• a literal range reference (like $Q$42:$Q$50)

• a named formula that itself resolves to a range reference

That last one is key - there is no way to have a VBA function just return an array that can be used for validation, even if you call it from a named formula.

You can write a VBA function that returns a range reference, though, and call that from a named formula. This can be useful as part of the following technique that approximates the ability to do what you actually want.

First, have an actual range somewhere that calls your arbitrary-array-returning VBA UDF. Say you had this function:

Public Function validationList(someArg, someOtherArg)

    'Pretend this got calculated somehow based on the above args...
    validationList = Array("a", "b", "c")
End Function

And you called it from $Q$42:$Q$50 as an array formula. You'd get three cells with "a", "b", and "c" in them, and the rest of the cells would have #N/A errors because the returned array was smaller than the range that called the UDF. So far so good.

Now, have another VBA UDF that returns just the "occupied" part of a range, ignoring the #N/A error cells:

Public Function extractSeq(rng As Range)

    'On Error GoTo EH stuff omitted...

    'Also omitting validation - is range only one row or column, etc.

    Dim posLast As Long
    For posLast = rng.Count To 1 Step -1
        If Not IsError(rng(posLast)) Then
            Exit For
        End If

        If rng(posLast) <> CVErr(xlErrNA) Then
            Exit For
        End If
    Next posLast

    If posLast < 1 Then
        extractSeq = CVErr(xlErrRef)
    Else
        Set extractSeq = Range(rng(1), rng(posLast))
    End If
End Function

You can then call this from a named formula like so:

=extractSeq($Q$42:$Q$50)

and the named formula will return a range reference that Excel will accept an allowable validation list. Clunky, but side-effect free!

Note the use of the keyword 'Set' in the above code. It's not clear from your question, but this might be the only part of this whole answer that matters to you. If you don't use 'Set' when trying to return a range reference, VBA will instead return the value of the range, which can't be used as a validation list.