private void ListView_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (e.AddedItems.Count == 0)
            {
                return;
            }

            _selectedTop = e.AddedItems[0] as Top;
            Top top = _selectedTop.Copy();

            SetControlsVisibility(Visibility.Hidden);

            if (_worker.IsBusy)
            {
                _worker.CancelAsync();
                return;
            }
            _worker.RunWorkerAsync(top);
        }