Handling event detection and intent

event-handling.vb

 Private LastActiveControl As Control = Me   ' initialize on form creation

    Protected Overrides Sub UpdateDefaultButton()
    ' Just added a IsNot condition to clarity
        If (LastActiveControl Is txtNumberOfDrinks) AndAlso
            ((ActiveControl Is btnClear) OrElse (ActiveControl Is btnExit)) Then
    ' Only problem is that it tries to validate twice upon tabbing away (only once on click)
        ElseIf (LastActiveControl Is txtNumberOfDrinks) AndAlso
        ((ActiveControl IsNot btnClear) OrElse (ActiveControl IsNot btnExit)) Then
            validateForm()
        End If

        LastActiveControl = ActiveControl   ' Store this for the next time Focus changes

    End Sub