private async void SelectionState_ActiveItemChanged(object sender, EventArgs e) { if (_selection.ActiveItem == null) { return; } if (!(_selection.ActiveItem.Data is FileEntity fileEntity)) { return; } var items = View.Items .SelectMany(pair => pair.Items) .Select(item => item.Data) .OfType <FileEntity>() .ToList(); var index = items.IndexOf(fileEntity); await _presentation.PreviewAsync(items, index); }