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

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). So I go Insert/Name/Define and create "REGNAMES" by simply assigning the formula above (no cell range). I then return to the Data/Validation and when I set Source like so:
=REGNAMES
Now I get "Source currently evaluates to error". Unfortunately, this error does not go away even after I ignore it. I can create a range formula in the sheet like so:
{=REGNAMES}
and drag this to the right across a couple cells and the rNames function faithfully returns
Option #1 | Options #2 | ...
That is, the function returns a range as intended.
I know that I can use macro code to manipulate the List setting for that cell out of VBA. I don't like these side-effects much. I would prefer a clean dependency tree built on functions. Any ideas how to get the Data/Validation to accept the array values returned from rNames?
Thanks.
PS: rNames returns the result range as a Variant, if that has any bearing.

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.

Answer 2

I was just doing some research on accessing the contents of a Shapes dropdown control, and discovered another approach to solving this problem that you might find helpful.
Any range that can have a validation rule applied can have that rule applied programmatically. Thus, if you want to apply a rule to cell A1, you can do this:
ActiveSheet.Range("A1").Validation.Add xlValidateList, , , "use, this, list"
The above adds an in-cell dropdown validation that contains the items "use," "this," and "list." If you override the Worksheet_SelectionChange() event, and check for specific ranges within it, you can call any number of routines to create/delete validation rules. The beauty of this method is that the list referred to can be any list that can be created in VBA. I needed a dynamically-generated list of an ever-changing subset of the worksheets in a workbook, which I then concatenated together to create the validation list.
In the Worksheet_SelectionChange() event, I check for the range and then if it matches, fire the validation rule sub, thus:
Private Sub Worksheet_SelectionChange(ByVal Target as Range)
If Target.Address = "$A$1" Then
UpdateValidation
End If
End Sub
The validation list-builder code in UpdateValidation() does this:
Public Sub UpdateValidation()
Dim sList as String
Dim oSheet as Worksheet
For Each oSheet in Worksheets
sList = sList & oSheet.Name & ","
Next
sList = left(sList, len(sList) -1) ' Trim off the trailing comma
ActiveSheet.Range("A1").Validation.Delete
ActiveSheet.Range("A1").Validation.Add xlValidateList, , , sList
End Sub
And now, when the user clicks the dropdown arrow, he/she will be presented with the updated validation list.

Answer 3

Sounds like your rNames function is probably returning a 1-dimensional array (which will be treated as a row).
Try making your function return a column as a 1-based 2-dimensional array (Ansa(1,1) then Ansa(2,1) etc)

Answer 4

Couln't you rather use dynamic range names ? That's quite easy and does not require any vba.

Answer 5

For the future:
Following is then used in a named range and the named range set as the 'Data Validation' 'List' value
Function uniqueList(R_NonUnique As Range) As Variant
Dim R_TempList As Range
Dim V_Iterator As Variant
Dim C_UniqueItems As New Collection
On Error Resume Next
For Each V_Iterator In R_NonUnique
C_UniqueItems.Add "'" & V_Iterator.Parent.Name & "'!" & V_Iterator.Address, CStr(V_Iterator.Value2)
Next V_Iterator
On Error GoTo 0
For Each V_Iterator In C_UniqueItems
If R_TempList Is Nothing Then
Set R_TempList = Range(V_Iterator)
End If
Set R_TempList = Union(R_TempList, Range(V_Iterator))
Next V_Iterator
Set uniqueList = R_TempList
End Function

Answer 6

#user5149293 I higly appreciate your code, but I recommend to prevent the collection from throwing an error, when adding duplicate values. The usage of a custom formula in the data validation list or in Name-Manager-Formula prevents the code from using the vbe debugger, which makes it very hard to trace back errors here (I ran into this problem myself, when using your code).
I recommend to check the existence of key in the collection with a separate function:
Function uniqueList(R_NonUnique As Range) As Variant
'Returns unique list as Array
Dim R_TempList As Range
Dim V_Iterator As Variant
Dim C_UniqueItems As New Collection
For Each V_Iterator In R_NonUnique
'Check if key already exists in the Collection
If Not HasKey(C_UniqueItems, V_Iterator.Value2) Then
C_UniqueItems.Add Item:="'" & V_Iterator.Parent.Name & "'!" & V_Iterator.Address, Key:=CStr(V_Iterator.Value2)
End If
Next V_Iterator
For Each V_Iterator In C_UniqueItems
If R_TempList Is Nothing Then
Set R_TempList = Range(V_Iterator)
End If
Set R_TempList = Union(R_TempList, Range(V_Iterator))
Next V_Iterator
Set uniqueList = R_TempList
End Function
Function HasKey(coll As Collection, strKey As String) As Boolean
'https://stackoverflow.com/questions/38007844/generic-way-to-check-if-a-key-is-in-a-collection-in-excel-vba
Dim var As Variant
On Error Resume Next
var = coll(strKey)
HasKey = (Err.Number = 0)
Err.Clear
End Function