Disabling or Enabling Listbox and Tree Control Items

Right-click a listbox or tree control item and select Disable Item from the shortcut menu to disable an item. Right-click a listbox or tree control item and select Enable Item from the shortcut menu to enable a disabled item.

You also can use the Disabled Items property to disable listbox items programmatically and the Active Item:Disabled? property to disable tree control items programmatically.