If you're using Windows Forms, perhaps the simplest way to realize your goal would be to handle the first combo box's
SelectedIndexChange event[
^] and disable the 2nd combo box (by setting its
Enabled
property to false) when the first combo box's selected item matches your logic.
If you're using WPF, I recommend binding the
IsEnabled
property of the 2nd combo box to a property in your view model, and setting that property to false when the property of the first combo box's
SelectedItem
binding changes to suit your logic. Of course, I'm assuming you're using MVVM, although the WinForms tack could be taken if you're using codebehind.
/ravi