protected override void OnViewLoaded()
{
base.OnViewLoaded();
Observable.FromEventPattern<TextSnapshotChangedEventArgs>(h => QueryDoc.TextChanged += h,
h => QueryDoc.TextChanged -= h)
.Throttle(TimeSpan.FromSeconds(0.5))
.TakeUntil(Unloaded)
.ObserveOnDispatcher()
.Subscribe(e => UpdateCollectionSource());
}