void OnSelectionChanged (object sender, EventArgs args)
{
List<Note> selected_notes = GetSelectedNotes ();
if (selected_notes == null || selected_notes.Count == 0) {
Tomboy.ActionManager ["OpenNoteAction"].Sensitive = false;
Tomboy.ActionManager ["DeleteNoteAction"].Sensitive = false;
} else if (selected_notes.Count > 0) {
Tomboy.ActionManager ["OpenNoteAction"].Sensitive = true;
Tomboy.ActionManager ["DeleteNoteAction"].Sensitive = true;
} else {
// Many notes are selected
Tomboy.ActionManager ["OpenNoteAction"].Sensitive = false;
Tomboy.ActionManager ["DeleteNoteAction"].Sensitive = true;
}
}