public DefaultFileSelectorBackend ()
{
filters = new FileDialogFilterCollection (null);
var box = new HBox ();
entry = new TextEntry ();
entry.Changed += (sender, e) => NotifyFileChange ();
box.PackStart (entry, true);
var btn = new Button ("...");
box.PackStart (btn);
btn.Clicked += BtnClicked;
Content = box;
}