Обнаружение Captive Portal с использованием решения @supports или только CSS

Я написал эту функцию для перемещения моих выбранных элементов:

using System.Collections;
using System.Collections.Generic;

private void MoveListboxItems(int step, ListBox lb) {
    /* 'step' should be:
     *   -1 for moving selected items up
     *    1 for moving selected items down
     * 'lb' is your ListBox
     *   see examples how to call below this function
    */
    try {
        // do only something when really an item is selected
        if (lb.SelectedIndex > -1) {
            // get some needed values - they change while we manipulate the listbox
            // but we need them as they was original
            IList SelectedItems = lb.SelectedItems;
            IList SelectedIndices = lb.SelectedIndices;

            // set some default values
            int selIndex = -1;
            int newIndex = -1;
            int selCount = SelectedItems.Count;
            int lc = 0;
            int mc = 0;
            string moveOldValue = string.Empty;
            string selectedItemValue = string.Empty;

            if (step == 1) {
                mc = selCount - 1;
            } else {
                mc = lc;
            }
            // enter the loop through the selected items
            while (lc < selCount) {
                selectedItemValue = string.Empty;
                moveOldValue = string.Empty;

                try {
                    // get the item that should get moved
                    selectedItemValue = SelectedItems[mc].ToString();
                    selIndex = Convert.ToInt32(SelectedIndices[mc]);
                } catch {
                    selIndex = -1;
                }
                // gen index for new place
                newIndex = selIndex + step;
                try {
                    // get the old value from the place where the item get moved
                    moveOldValue = lb.Items[newIndex].ToString();
                } catch { /* do nothing */ }
                try {
                    if (!String.IsNullOrEmpty(selectedItemValue) && !String.IsNullOrEmpty(moveOldValue) && selIndex != -1 && newIndex != -1 && !lb.SelectedIndices.Contains(newIndex)) {
                        // move selected item
                        lb.Items.RemoveAt(newIndex);
                        lb.Items.Insert(newIndex, selectedItemValue);
                        // write old value back to the old place from selected item
                        lb.Items.RemoveAt(selIndex);
                        lb.Items.Insert(selIndex, moveOldValue);
                        // hold the moved item selected
                        lb.SetSelected(newIndex, true);
                    }
                } catch { /* do nothing */ }
                lc++;
                if (step == 1) {
                    mc -= step;
                } else {
                    mc = lc;
                }
            }
        }
    } catch { /* do nothing */ };
}

// examples how i call the function above
void BtnLbUp_Click(object sender, EventArgs e) {
    MoveListboxItems(-1, this.lbMyList);
}

void BtnLbDown_Click(object sender, EventArgs e) {
    MoveListboxItems(1, this.lbMyList);
}