Ultimately here is what I did to solve my problem. I don't know if there are any pitfalls in the way I am doing it but it seems to be working. The combobox is restricted to only predefined pulldown items.
Private Sub Window_Loaded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
Private Sub ComboBox1_SelectionChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs) Handles ComboBox1.SelectionChanged
Dim indexnum As Integer = ComboBox1.SelectedIndex
MsgBox(indexnum & " " & ComboBox1.Items(indexnum))
This is test code but it proves the concept I think.