class Listener4Assist implements ListenerAssist {

    public void fetchEnd(DownloadTask task, int blockIndex) {
        final Listener4Model model = modelHandler.getOrRecoverModel(task, task.getInfo());
        if (model == null) return;

        if (assistExtend != null
                && assistExtend.dispatchBlockEnd(task, blockIndex, model)) {
            return;
        }

        if (callback != null) {
            callback.blockEnd(task, blockIndex, model.info.getBlock(blockIndex));
        }
    }

      Listener4Assist(ListenerModelHandler<T> handler);
    public  Listener4Assist(ListenerModelHandler.ModelCreator<T> creator);

}