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

@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