private void listbox_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            e.Handled = true;
            xxxDataSourceItem item = GetElementFromPoint(listbox, e.GetPosition(listbox));
            listbox.SelectedItem = item;
        }

        private xxxDataSourceItem GetElementFromPoint(ListBox box, Point point)
        {
            IInputElement elementobj = box.InputHitTest(point);

            UIElement element = elementobj as UIElement;
            if (element != null)
            {
            while (true)
            {
            if (element == box)
            {
            return null;
            }
            object item = box.ItemContainerGenerator.ItemFromContainer(element);
            bool itemFound = !(item.Equals(DependencyProperty.UnsetValue));
            if (itemFound)
            {
                return item as xxxDataSourceItem;
            }
            element = (UIElement)VisualTreeHelper.GetParent(element);
            }
            }
            return null;
        }