ICollectionView

        this.lcv = new ListCollectionView(s);
        this.listBox.ItemsSource = this.lcv;

        this.filterFx = (p) => ((string)p).ToUpper().Contains(this.textBox.Text.ToUpper());
        lcv.Filter = this.filterFx;
 

        lcv.Refresh();

        if (lcv.Count == 0)
            lcv.Filter = null;
        else
            lcv.Filter = filterFx;