线程同步

Question

我有一个描述RecyclerView的片段类。创建元素需要array。array是通过解析JSON形成的。当我使用良好的互联网连接，一切都好，我可以看到理想的项目清单。但是使用低速连接，我的UI是空的。

我意识到threads存在一些问题，但是我没有足够的知识来解决我的问题。

这是一个代码：

public class ListVideo extends Fragment {
private int loadLimit = 9;
private RecyclerView recyclerView;
private RecyclerAdapter adapter;
private LinearLayoutManager linearLayoutManager;
final OkHttpClient client = new OkHttpClient();
List<VideoData> videoList;
List<String> videoDataList;
JSONArray json_array_list_of_videos;
int counter = 0;
int offset;

@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {
    return inflater.inflate(R.layout.listvideofragment, container, false);
}

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    videoList = new ArrayList<>();
    videoDataList = new ArrayList<>();
    recyclerView = (RecyclerView) view.findViewById(R.id.list);

    loadData(offset);
    createRecycleView();
    recyclerView.addOnScrollListener(new EndlessRecyclerOnScrollListener(
            linearLayoutManager) {
        @Override
        public void onLoadMore(int offset) {
            // do somthing...

            loadMoreData(offset);

        }

    });


}

private void loadMoreData(int offset) {

    loadLimit += 10;
    loadData(offset);

    adapter.notifyDataSetChanged();

}

private void loadData(final int offset) {
    try {
        Request request = new Request.Builder()
                .url("http://video.motti.be/api/video.getVideoList?offset=" +
                        offset
                        + "&limit=20")
                .build();

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Request request, IOException throwable) {
                throwable.printStackTrace();
            }

            @Override
            public void onResponse(Response response) throws IOException {
                try {
                    if (!response.isSuccessful())
                        throw new IOException("Unexpected code " + response);

                    Headers responseHeaders = response.headers();
                    for (int i = 0; i < responseHeaders.size(); i++) {
                        System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
                    }

                    String json_string_obj = response.body().string();
                    JSONObject url = new JSONObject(json_string_obj);
                    json_array_list_of_videos = url.getJSONArray("data");
                    System.out.println(json_array_list_of_videos.toString());
                    for (int y = 0; y <= 9; y++) {
                        if (json_array_list_of_videos.get(y).toString().equals("A9knX0GXrg")) {
                            videoDataList.add("6kS9Tt1e47g");
                        } else {
                            videoDataList.add(json_array_list_of_videos.get(y).toString());
                            System.out.println("++++++" + json_array_list_of_videos.get(y).toString());
                        }
                    }
                    for (int i = counter; i <= loadLimit; i++) {
                        if (videoDataList == null) {
                            return;
                        } else {
                            VideoData next_queue_id = new VideoData(videoDataList.get(i));
                            videoList.add(next_queue_id);
                            counter++;

                        }
                    }


                } catch (Exception e) {
                    e.printStackTrace();
                }

            }
        });

    } catch (ArrayIndexOutOfBoundsException e) {
        e.printStackTrace();

    }

}

public void createRecycleView() {

    adapter = new RecyclerAdapter(videoList, getContext());
    linearLayoutManager = new LinearLayoutManager(getActivity());
    linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(linearLayoutManager);
    recyclerView.setAdapter(adapter);
}
}

我明白了，后来我得到了Response的new adapter creates.For缺乏知识，当我难过的时候，我不知道如何用onResponse方法来做thread等。

希望你不会觉得这个问题无聊或愚蠢，并会帮助我。

提前谢谢你！

Answer 1

修改适配器列表(videoList)后，需要通知适配器。

目前，loadMoreData(int offset)方法不能保证，因为loadData(offset);方法可以在修改列表之前返回(请求是异步处理的)。

你能做的就是：

从adapter.notifyDataSetChanged();方法中删除loadMoreData(int offset)语句，并将其添加到onResponse(Response response)方法中。

示例：

@Override
public void onResponse(Response response) throws IOException {
    try {
        ...
        for (int i = counter; i <= loadLimit; i++) {
            if (videoDataList == null) {
                return;
            } else {
                VideoData next_queue_id = new VideoData(videoDataList.get(i));
                videoList.add(next_queue_id);
                counter++;
            }
        }
        ListVideo.this.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                adapter.notifyDataSetChanged();
            }
        });
    } catch (Exception e) {
        e.printStackTrace();
    }
}

这种方法可能会产生其他问题，因为videoList可以由多个线程同时修改。您需要找到一种方法来同步对此列表的访问或使用线程安全列表。