class Listener1Assist implements ListenerAssist,
        ListenerModelHandler.ModelCreator<Listener1Assist.Listener1Model> {

    public void fetchProgress(DownloadTask task, long increaseBytes) {
        final Listener1Model model = modelHandler.getOrRecoverModel(task, task.getInfo());
        if (model == null) return;

        model.currentOffset.addAndGet(increaseBytes);
        if (callback != null) callback.progress(task, model.currentOffset.get(), model.totalLength);
    }

    public  Listener1Assist();
      Listener1Assist(ListenerModelHandler<Listener1Model> handler);

}