Question

我制作的应用程序使用外部API显示足球联赛的表格。我正在处理一个片段，其中包含一个recyclerview（显示联盟表），我使用AsyncTask从Web获取实际数据。我有两个问题：

在片段的onCreateView方法中，我设置了recyclerview。我把适配器作为局部变量，然后，在AsyncTask中的onPostExecute方法中，我将结果（表数据。在这里，它是TeamLeagueStandings的数组）传递给适配器。然后，问题是适配器由于某种原因保持为空，我无法理解为什么。
在获取数据时，我希望它显示progressBar，在AsyncTask方法中，onPreExecute和onPostExecute，我更改进度条的可见性值。出于某种原因，进度条根本没有出现。为什么会这样？

这是片段，其中包含recyclerview（用于显示表本身），以及其中的AsyncTask（DownloadTask）：

 public class TableStandingsFragment extends Fragment {
    private static final String LEAGUETOLAUNCH = "league";
    private TeamAdapter adapter;
    private ProgressBar progressBar;
    private String league;
    private OnFragmentInteractionListener mListener;

    public TableStandingsFragment() {
        // Required empty public constructor
    }


    public static TableStandingsFragment newInstance(String param1) {
        TableStandingsFragment fragment = new TableStandingsFragment();
        Bundle args = new Bundle();
        args.putString(LEAGUETOLAUNCH, param1);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        // Gets the argument of the fragment. This will tell us which league table to show
        //using the method "GeturlTeamsByArg", which gives the URL, and then using AsyncTask to get
        //the actual data, with the given url.
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            league = getArguments().getString(LEAGUETOLAUNCH);
        }
    }



    public URL GeturlTeamsByArg() {

        //Returns the correct URL of the required league table, depends on the variable "league"

        URL url=null;
        if (league == "" || league == null)
            return null;
        switch (league) {
            case ("Premier League"):
                url = League_standings.GetPLQuery();
                break;
            case ("Football League Championship"):
                url = League_standings.GetChampionshipQuery();
                break;
            case ("Eredvise"):
                url = League_standings.GetEredviseQuery();
                break;
            case ("Ligue 1"):
                url = League_standings.GetLigue1Query();
                break;
            case ("Ligue 2"):
                url = League_standings.GetLigue2Query();
                break;
            case ("Bundesliga"):
                url = League_standings.GetBundesligaQuery();
                break;
            case ("2. Bundesliga"):
                url = League_standings.GetSecBundesligaQuery();
                break;
            case ("Primera División"):
                url = League_standings.GetSpanishQuery();
                break;
            case ("Serie A"):
                url = League_standings.GetSeriaAQuery();
                break;
            case ("Primeira Liga"):
                url = League_standings.GetPortugeseQuery();
                break;
        }
        return  url;
    }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
           // StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            //StrictMode.setThreadPolicy(policy);
            View v= inflater.inflate(R.layout.fragment_recyclerview, container, false);
            progressBar = v.findViewById(R.id.progressBar);
            DownloadTask downloadTask=new DownloadTask();
            try{
                downloadTask.execute(GeturlTeamsByArg());
                RecyclerView recyclerView =  (RecyclerView) v.findViewById(R.id.recyler_teams);
                recyclerView.setHasFixedSize(true);
                recyclerView.setAdapter(adapter);
                recyclerView.addItemDecoration(new VerticalSpaceItemDecorator(30));
                LinearLayoutManager layoutManager = new LinearLayoutManager(getContext());
                layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
                recyclerView.setLayoutManager(layoutManager);
                }
            catch (Exception e){
                Log.d("error",e.toString());
            }




            return v;
        }


    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }
    class VerticalSpaceItemDecorator extends RecyclerView.ItemDecoration {

        private final int spacer;

        public VerticalSpaceItemDecorator(int spacer) {
            this.spacer = spacer;
        }

        @Override
        public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
            super.getItemOffsets(outRect, view, parent, state);
            outRect.bottom = spacer;
        }
    }

    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }



    public class DownloadTask extends AsyncTask<URL, Void, TeamLeagueStandings[]> {

        // COMPLETED (26) Override onPreExecute to set the loading indicator to visible
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
           progressBar.setVisibility(View.VISIBLE);
        }

        @Override
        protected TeamLeagueStandings[] doInBackground(URL... params) {
            URL searchUrl = params[0];
            TeamLeagueStandings[] results = null;
            try {
                results = League_standings.LeagueStandingsArray(searchUrl);
            } catch (IOException e) {
                e.printStackTrace();
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return results;
        }

        @Override
        protected void onPostExecute(TeamLeagueStandings[] results) {
            progressBar.setVisibility(View.INVISIBLE);
            adapter=new TeamAdapter(results);

        }
    }
  }

这是我获取实际数据并处理JSON的类：

public class League_standings {

//League codes in the url
private final static int PLCODE = 445;
private final static int CHAMPIONSHIPCODE = 446;
private final static int EREDVISECODE = 449;
private final static int LIGUE1CODE = 450;
private final static int LIGUE2CODE = 451;
private final static int BUNDESLIGACODE = 452;
private final static int SECBUNDESLIGACODE = 453;
private final static int SPANISHCODE = 455;
private final static int SERIAACODE = 456;
private final static int PORTUGESECODE = 457;
private static String nationCode = "";
private static String querystr = "";
private static URL url = null;
private static TeamLeagueStandings[] teams;


public static URL GetPLQuery() {
    // Returns the full URL of the search query combined with the PL code.
    nationCode = Integer.toString(PLCODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}

public static URL GetChampionshipQuery() {
    // Returns the full URL of the search query combined with the championship code.
    nationCode = Integer.toString(CHAMPIONSHIPCODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}

public static URL GetEredviseQuery() {
    // Returns the full URL of the search query combined with the eredvise code.
    nationCode = Integer.toString(EREDVISECODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}

public static URL GetLigue1Query() {
    // Returns the full URL of the search query combined with the ligue1 code.
    nationCode = Integer.toString(LIGUE1CODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}

public static URL GetLigue2Query() {
    // Returns the full URL of the search query combined with the ligue2 code.
    nationCode = Integer.toString(LIGUE2CODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}

public static URL GetBundesligaQuery() {
    // Returns the full URL of the search query combined with the bundesliga code.
    nationCode = Integer.toString(BUNDESLIGACODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}

public static URL GetSecBundesligaQuery() {
    // Returns the full URL of the search query combined with the second bundesliga code.
    nationCode = Integer.toString(SECBUNDESLIGACODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}

public static URL GetSpanishQuery() {
    // Returns the full URL of the search query combined with the Spanish league code.
    nationCode = Integer.toString(SPANISHCODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}

public static URL GetSeriaAQuery() {
    // Returns the full URL of the search query combined with the seria A code.
    nationCode = Integer.toString(SERIAACODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}

public static URL GetPortugeseQuery() {
    // Returns the full URL of the search query combined with the Portugese league code.
    nationCode = Integer.toString(PORTUGESECODE);
    querystr = "competitions/" + nationCode + "/leagueTable";
    url = Data.BuildUrl(querystr);
    return url;
}


public static TeamLeagueStandings[] LeagueStandingsArray(URL url) throws IOException, JSONException {

    //Gets the full url of the requested league table, should look like: 
    //"http://api.football-data.org/v1/competitions/445/leagueTable"
    //Processing the JSON data from the API, then returns an array which 
    //contains the teams of the league
    //that was requested, in THE ORDER OF THE TABLE!!!

    String results = Data.GetResponseFromHttpUrl(url);
    JSONObject resultsJSON = new JSONObject(results);
    JSONArray teamsJson = resultsJSON.getJSONArray("standing");
    int length = teamsJson.length();
    teams = new TeamLeagueStandings[length];
    // name,games,wins,draws,losses,GD,points, pic
    for (int i = 0; i < length; i++) {


        JSONObject object = teamsJson.getJSONObject((i));
        TeamLeagueStandings team = new TeamLeagueStandings();
        team.setPlace(Integer.toString(object.getInt("position")));
        team.setTeamName(object.getString("teamName"));
        team.setCurGames(Integer.toString(object.getInt("playedGames")));
        team.setWins(Integer.toString(object.getInt("wins")));
        team.setDraws(Integer.toString(object.getInt("draws")));
        team.setLosses(Integer.toString(object.getInt("losses")));
        team.setGoalDifference(Integer.toString(object.getInt("goalDifference")));
        team.setPoints(Integer.toString(object.getInt("points")));
        team.setImgString(object.getString("crestURI"));
        if (team.getTeamName().toLowerCase().contains("FC".toLowerCase())) {
            team.setTeamName(team.getTeamName().replace("FC", ""));
        }
        if (team.getTeamName().endsWith(" ")) {
            team.setTeamName(StringUtils.strip(team.getTeamName()));

        }
        if (team.getTeamName().length() > 12) {
            String name = team.getTeamName();
            for (int j = 12; j < name.length(); j++) {
                char c = name.charAt(j);
                if (c == ' ') {
                    name = name.substring(0, j) + "\n" + name.substring(j + 1);
                    team.setTeamName(name);
                    break;
                }
            }
        }
        teams[i] = team;
    }

    return teams;
}

}

谢谢！：）

Answer 1

您可以在doinBackground期间使用获取数据onProgressUpdate func .. 例如：

class MyTask extends AsyncTask<Void, Void, Void> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected Void doInBackground(Void... voids) {
            onProgressUpdate();
            return null;
        }

        @Override
        protected void onProgressUpdate(Void... values) {
            super.onProgressUpdate(values);
            // here you can get data from MainThread
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
        }
    }

Android studio-从AsynTask获取数据到主线程

1 个答案: