Setting the Number of Selections a User Can Select in Listboxes
You can set the number of selections a user can select in a listbox interactively or programmatically.
Complete the following steps to specify how many items you can select in a listbox at a time.
On the front panel, right-click the listbox.
Select Selection Mode from the shortcut menu and select from the following options:
1 Item(Default) One item in the listbox always is selected (highlighted). When you click a different item, the new item is selected (highlighted), and the previous item is deselected.
0 or 1 ItemThe behavior is the same as for 1 Item, except that a user can deselect the current item by <Shift>-clicking it, leaving no items selected. You can use Item Dragging to move items in the listbox by dragging them with the cursor.
0 or More ItemsThe user can select multiple items.
1 or More ItemsThe user can select multiple items, but at least one item must be selected.