title: CollectionViewSource with Sort get sorted Items
body: <p>I have a <code>datagrid</code> which has as source <code>CollectionViewSource</code> with custom sorting and I need to get sorted items collection as can be seen in datagrid. I can get sorted description and sort source collection, but I need this collection many time.</p>
  
  <p>Is there some way how to get sorted collection which enable indexation (<code>item[index])</code>?</p>