Calling Where() on an observable collection returns a WhereEnumerator which is a non-observable enumerator that just walks the given collection. It will not notify its destination if the source changes.
this.groupTreeListView.ItemsSource = loadOperation.Entities.Where(t => t.ParentGroup == null);
There is a way to achieve this using a CollctionView:
var collectionView =
collectionView.Source = loadOperation.Entities;
collectionView.Filter += (s, e) => (e.Item
.groupTreeListView.ItemsSource = collectionView;
Hopefully this will help you,
the Telerik team
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