How to set data validation to BLANKs?

[boim]

Let's say I have two columns A and B. I'd like to set data validation on B as follows:
-If corresponding row in A is some text then show list of valid input.
-If corr. row in A is blank then list of valid input is empty.

How do I do that?

Thank you.

 

[lenze]

Not sure if this is better, but it is different and will annoy the heck out of the users

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Count > 1 Then Exit Sub
If Target.Column <> 2 Then Exit Sub
If Target.Offset(0, -1) = "" Then
     MsgBox "You moron!!. You can enter a value until " & Target.Offset(0, -1).Address & " is filled in!!!"
     With Application
       .EnableEvents = False
       .Undo
       .EnableEvents = True
     End With
End If
End Sub

lenze

 

[boim]

Thanks lenze, however the blanks in A is there purposefully.

Here is related post where I tried and got error:
http://www.mrexcel.com/forum/showthread.php?t=445657

Still thinking of how to do this nicely, for ex: fill column A with some thing and add data validation, next is to clear A, and then fill with real data. However, I feel this approach is not quite safe since it seems like exploiting some kind of loophole/bug.