title: C# listbox select and unselect item in MultiExtended mode
body: <p>When I click on a unselected item in a listbox it will be selected. The client wants that if you click again (so without using the cntrl key) it deselects.</p>
  
  <p>But I tried many things but nothing works. So is this possible and if possible can some one explain me how by using some C# code?</p>