执行异步任务时，滑动刷新会冻结

Question

我遇到了一个问题，当我尝试使用刷卡刷新布局在刷新时运行异步任务时，它会“冻结”并且不会旋转。任务完成后，它就会消失。

这是我的代码：

HotActivityFragment.java：

public class HotActivityFragment extends Fragment {

    ListView hotList;
    SwipeRefreshLayout mSwipeRefreshLayout;
    Context context;
    SharedPreferences sharedPreferences;
    HotListAdapter hotListAdapter;
    public HotActivityFragment() {

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.fragment_hot, container, false);
        context = getContext();
        mSwipeRefreshLayout = (SwipeRefreshLayout)view.findViewById(R.id.activity_main_swipe_refresh_layout);
        hotList = (ListView)view.findViewById(R.id.hotListView);
        hotList.setOnScrollListener(new EndlessScrollListener(getActivity()));
        sharedPreferences = getActivity().getPreferences(Context.MODE_PRIVATE);
        try {
            ArrayList<ListTypeItem> initial_list = new DownloadPosts(getActivity()).execute().get();
            this.hotListAdapter = new HotListAdapter(getContext(), initial_list);
            hotList.setAdapter(hotListAdapter);
        }catch(Exception e)
        {
            Log.d("Download Error", e.toString());
        }
        mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                retrievePosts();
            }

        });
        mSwipeRefreshLayout.setColorSchemeResources(R.color.accentColor, R.color.backgroundColor);



        return view;
    }
    public void retrievePosts()
    {
        // showing refresh animation before making http call
        mSwipeRefreshLayout.setRefreshing(true);

        //shared preferences = empty
        sharedPreferences.edit().putString("last_time_downloaded", "empty").commit();
        try {
            ArrayList<ListTypeItem> listItems = new DownloadPosts(getActivity(), mSwipeRefreshLayout).execute().get();
            hotListAdapter.updateList(listItems);
            hotListAdapter.notifyDataSetChanged();
        } catch (Exception e) {
            Log.d("Download Error", e.toString());
        }

        mSwipeRefreshLayout.setRefreshing(false);

        //for testing purposes
//        new Handler().postDelayed(new Runnable() {
//            @Override public void run() {
//                mSwipeRefreshLayout.setRefreshing(false);
//            }
//        }, 5000);
    }
    }

DownloadPosts.java：

public class DownloadPosts  extends AsyncTask<Void, Void, ArrayList<ListTypeItem>> {

    SharedPreferences sharedPreferences;
    SwipeRefreshLayout swipeRefreshLayout;

    public DownloadPosts(Activity activity)
    {
        this.sharedPreferences = activity.getPreferences(Context.MODE_PRIVATE);
    }
    public DownloadPosts(Activity activity, SwipeRefreshLayout swipeRefreshLayout)
    {
        this.sharedPreferences = activity.getPreferences(Context.MODE_PRIVATE);
        this.swipeRefreshLayout = swipeRefreshLayout;
    }
    @Override
    protected ArrayList<ListTypeItem> doInBackground(Void... args)
    {
        StringBuilder parsedString = new StringBuilder();

        ArrayList<ListTypeItem> downloadList = new ArrayList<>();
        StringBuilder str = new StringBuilder();

        if(sharedPreferences.getBoolean("Thomas More",false))
        {
            str.append("190155257998823,");
        }

        String school_url = str.toString();
        if(school_url.length() > 0)
        {
            school_url = school_url.substring(0, str.length()-1);
        }
        try{
            String date = "";
            //checken of opnieuw moet bepaald worden
            // + in de adapter moet als gereload wordt last_time_downloaded == empty
            if(!sharedPreferences.getString("last_time_downloaded","empty").equals("empty"))
            {
                String last_date = sharedPreferences.getString("last_time_downloaded","nothing");
                last_date = last_date.replace(" ","T");
                date= "&datum_last_posted=" + last_date;
            }
            URL url = new URL("http://localhost/getpostlist.php?school_post=" + school_url + date);
            URLConnection conn = url.openConnection();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String json;
            while((json = bufferedReader.readLine())!= null)
            {
                parsedString.append(json + "/n");
            }
            String s = parsedString.toString().trim();
            //converten van string opgehaald via http naar jsonobject
            JSONArray array = new JSONArray(s);
            for(int i = 0; i < array.length(); i++)
            {
                JSONObject tempObj = array.getJSONObject(i);
                School_WithoutImage tempSchool = new School_WithoutImage(tempObj.getString("school_id"),
                        tempObj.getString("post_message"),tempObj.getInt("views"),tempObj.getInt("likes")
                        ,tempObj.getInt("post_id"),tempObj.getString("datum_posted"));
                downloadList.add(tempSchool);
                if(i == array.length()-1) {
                    sharedPreferences.edit().putString("last_time_downloaded",tempObj.getString("datum_posted")).commit();
                }
            }
            JSONObject obj = array.getJSONObject(0);
        }catch(Exception e)
        {
            Log.d("Exception", e.toString());
        }

        return downloadList;
    }
    @Override
    protected void onPostExecute(ArrayList<ListTypeItem> result)
    {
        if(this.swipeRefreshLayout != null)
        {
//            swipeRefreshLayout.setRefreshing(false);
        }
    }

}

我不知道为什么swiperefreshview不会旋转。有人有想法吗？

Answer 1

因为呼叫get()：

.execute().get()

强制UI线程等待AsyncTask完成。

相反，您应该在onPostExecute方法中执行此操作：

 protected void onPostExecute(ArrayList<ListTypeItem> listItems) {
      hotListAdapter.updateList(listItems);
      hotListAdapter.notifyDataSetChanged();
 }

Answer 2

因为您正在等待来自asynctask的结果，只需在执行后调用get。并进一步将其传递给列表。

您可以使用本地广播侦听器或者可以创建一个界面，并将其作为回调，而不会冻结UI