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);
}