Getting dynamic dropdown list in VBA validation - vba

Question

I have the following case:
1.Column D populated with about 100 values,
2. Using these I create a validation in the Column A cells
3. If I have a value in Cell "A1", this particular value should not appear
in Cell "A2" dropdown list, now the values in "A1" and "A2" should not appear in "A3" and so on.
What should be the thought process to write the VBA code for this?

Answer 1

I found this one interesting, so check this out... Should work as you expect it...
Post this code into your Worksheet and adapt it for your needs (if necessary). Hope it helps.
Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
Dim ws As Worksheet
Dim dict As Object
Dim dictAlreadyTaken As Object
Dim valueRange As Range
Dim targetRange As Range
Dim cell As Object
Dim Key As Variant
Dim currentList() As Variant
Dim i As Integer
If Target.Column = 1 Then
Set ws = Worksheets(1)
Set dict = CreateObject("Scripting.Dictionary")
Set dictAlreadyTaken = CreateObject("Scripting.Dictionary")
Set valueRange = ws.Range("D:D")
Set targetRange = ws.Range("A:A")
For Each cell In valueRange
If cell.Value <> "" Then
dict.Add cell.Value, cell.Row
Else
Exit For
End If
Next cell
For Each cell In targetRange
If cell.Row <= dict.Count Then
If cell.Value <> "" Then
'ad the value taken
dictAlreadyTaken.Add cell.Value, cell.Row
End If
Else
Exit For
End If
Next cell
For Each cell In targetRange
If cell.Row <= dict.Count Then
'add this list
Erase currentList
ReDim currentList(0)
i = 0
ws.Cells(cell.Row, 1).Validation.Delete
For Each Key In dict.keys
If Not dictAlreadyTaken.exists(Key) Then
i = i + 1
ReDim Preserve currentList(i) As Variant
currentList(i) = Key
End If
Next Key
If UBound(currentList) > 0 Then
ws.Cells(cell.Row, 1).Validation.Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:=xlBetween, Formula1:=Join(currentList, ",")
End If
Else
Exit For
End If
Next cell
End If
End Sub

Answer 2

My thought process would be:
First loop to list all the ranges we need to compare:
Cells(1,1) should not appear in Range(Cells(1,4),Cells(1,4))
Cells(2,1) should not appear in Range(Cells(1,4),Cells(2,4))
Cells(3,1) should not appear in Range(Cells(1,4),Cells(3,4)) ...etc...
Easy enough. Now that we know what ranges to compare, loop through the comparisons:
re: Cells(3,1) should not appear in Range(Cells(1,4),Cells(3,4)) :
.
Dim c as range
For Each c in Range(Cells(1,4),Cells(3,4))
If c.Value = Cells(1,4).Value then
'it's a match! Delete it (or whatever)
c.Value = ""
End If
Next c
Finally, put the two loops together...
From what I understand of your description, I came up with this:
Sub compareCells()
Dim c As Range, x As Integer
For x = 1 To 10
Debug.Print "Cells(" & x & ",1) should not appear in Range(Cells(1,4),Cells(" & x & ",4))"
For Each c In Range(Cells(1, 4), Cells(x, 4))
Debug.Print "compare " & Cells(x, 1).Address & " to " & c.Address
If Cells(x, 1).Value = c.Value Then
Cells(x, 1).Cells.Font.Color = vbBlue
End If
Next c
Next x
End Sub
It should be easily adaptable to your needs, or if not, there are plenty of existing solutions & resources, even a Stack Overflow tag: cascadingdropdown

Answer 3

Here is an approach:
Select a column in your sheet that you can use for a named range (this column can be hidden). For the purpose of example below, I've used column J and my named range is called ValidationRange. I have also assumed that the values in your worksheet start from row 2.
Now in a module, add the following sub:
Sub SetDropDownRange()
Dim oNa As Name: Set oNa = ThisWorkbook.Names.Item("ValidationRange")
Dim iLR&, iC&, iLRJ&
Dim aDRange As Variant
Dim aVRRange As Variant
With ThisWorkbook.Worksheets("Sheet12")
iLR = .Range("D" & .Rows.count).End(xlUp).Row
iLRJ = .Range("J" & .Rows.count).End(xlUp).Row
aDRange = Range("D2:D" & iLR)
For iC = LBound(aDRange) To UBound(aDRange)
If Len(Trim(aDRange(iC, 1))) <> 0 Then
If Application.WorksheetFunction.CountIf(Range("A:A"), aDRange(iC, 1)) = 0 Then
If IsArray(aVRRange) Then
ReDim Preserve aVRRange(UBound(aVRRange) + 1)
Else
ReDim aVRRange(0)
End If
aVRRange(UBound(aVRRange)) = aDRange(iC, 1)
End If
End If
Next
End With
Range("J2:J" & iLRJ).Value = ""
Range("J2:J" & UBound(aVRRange) + 2).Value = Application.Transpose(aVRRange)
oNa.RefersTo = oNa.RefersToRange.Resize(UBound(aVRRange) + 1, 1)
End Sub
Now call this function when something changes in your worksheet.. like so:
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Column = 1 Or Target.Column = 4 Then
SetDropDownRange
End If
End Sub
Set Data Validation for the cells in column A using the named range (which is ValidationRange for this example)
Now everytime your select a value in column A, it will remove that value from the named range and hence from your dropdown box