int CompareDates (Gtk.TreeModel model, Gtk.TreeIter a, Gtk.TreeIter b)
{
Note note_a = (Note) model.GetValue (a, 3 /* note */);
Note note_b = (Note) model.GetValue (b, 3 /* note */);
if (note_a == null || note_b == null)
return -1;
else
return DateTime.Compare (note_a.ChangeDate, note_b.ChangeDate);
}