- crear canal (notification manager) en el MyApp y lo llamamos en el onCreate

    private void createNotificationManager() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            CharSequence name = getString(R.string.channel_name);
            String description = getString(R.string.channel_description);
            int importance = NotificationManager.IMPORTANCE_DEFAULT;
            NotificationChannel channel = new NotificationChannel(NOTIFICATION_CHANNEL_ID, name, importance);
            channel.setDescription(description);
            NotificationManager notificationManager = getSystemService(NotificationManager.class);
            notificationManager.createNotificationChannel(channel);
        }
    }

- lanzar notificacion, en la activity de turno
	Intent intent = new Intent(this, FavoritosActivity.class);
	buildNotification("Anadido Favorito", "parada " + favorito.getTrayecto().getParada().getCodigo() + "" +
                " - " + favorito.getTrayecto().getParada().getNombre(),
        PendingIntent.getActivity(this, 0, intent, 0));