Every time the choice list's status changes, e.g. when the user opens or
closed the list or selects an item from the list, the client application is
informed through the MCoeControlObserver interface. 
Notifications are received by the HandleControlEventL callback
function in the class MCoeControlObserver. The event is EEventStateChanged.
After receiving the event, the client application can use the choice list's SelectedIndex method
to request if the selection has changed. 
void CMyAppContainer::HandleControlEventL( CCoeControl* aControl,
                                                  TCoeEvent aEventType )
    {
     if ( aControl == iChoiceList )
        {
        switch ( aEventType )
            {
            case EEventStateChanged:
                {
                TInt newSelection = iChoiceList->SelectedIndex();
                if ( iSelection != newSelection )
                    {
                    // selected item changed
                    iSelection = newSelection;
                    }
                }
                break;
                    
            default:
                break;
            }
        }
    }