android - 如果数据已经加载，则停止从 .json 加载数据

Question

我有 2 个 fragment ( fragment A 和 fragment B)，具有使用 .json 加载数据的功能。

当我点击 fragment A 时，数据将会加载，而当我点击 fragment B 时，数据也会加载。

当我再次点击 fragment A 时，数据会重新加载并复制(附加上第一次点击的数据)。

如果数据已加载，如何停止加载数据？

示例图片 这是我的 fragment 代码

fragment _a.java

public class fragment_a extends Fragment {
    // Log tag
    private static final String TAG = MovieFragment1.class.getSimpleName();

    // Movies json url
    private static final String url = "http://.......";
    private ProgressDialog pDialog;
    private List<Movie> movieList = new ArrayList<Movie>();
    private ListView listView;
    private CustomListAdapter adapter;

    public MovieFragment1() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        hidePDialog();
    }

    private void hidePDialog() {
        if (pDialog != null) {
            pDialog.dismiss();
            pDialog = null;
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.activity_list, container, false);
        // Inflate the layout for this fragment

        final ListView listView = (ListView) rootView.findViewById(R.id.list);
        adapter = new CustomListAdapter(getActivity(), movieList);
        listView.setAdapter(adapter);

        pDialog = new ProgressDialog(getActivity());
        // Showing progress dialog before making http request
        pDialog.setMessage("Loading...");
        pDialog.show();


        // Creating volley request obj
        JsonArrayRequest movieReq = new JsonArrayRequest(url,
                new Response.Listener<JSONArray>() {
                    @Override
                    public void onResponse(JSONArray response) {
                        Log.d(TAG, response.toString());
                        hidePDialog();

                        // Parsing json
                        for (int i = 0; i < response.length(); i++) {
                            try {

                                JSONObject obj = response.getJSONObject(i);
                                Movie movie = new Movie();
                                if (obj.getString("tipe").equals("chest")){
                                movie.setTitle(obj.getString("name"));
                                movie.setThumbnailUrl(obj.getString("images1"));
                                //movie.setDescribe(obj.getString("describe"));
                                //movie.setRating(((Number) obj.get("rating"))
                                //        .doubleValue());
                                movie.setYear(obj.getInt("id"));
                                movie.setTipe(obj.getString("tipe"));

                                /*// Genre is json array
                                JSONArray genreArry = obj.getJSONArray("genre");
                                ArrayList<String> genre = new ArrayList<String>();
                                for (int j = 0; j < genreArry.length(); j++) {
                                    genre.add((String) genreArry.get(j));
                                }
                                movie.setGenre(genre);*/

                                // adding movie to movies array
                                movieList.add(movie);
                            }
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }

                        }

                        // notifying list adapter about data changes
                        // so that it renders the list view with updated data
                        adapter.notifyDataSetChanged();
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                VolleyLog.d(TAG, "Error: " + error.getMessage());
                hidePDialog();

            }
        });

        // Adding request to request queue
        AppController.getInstance().addToRequestQueue(movieReq);

        return rootView;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
    }

    @Override
    public void onDetach() {
        super.onDetach();
    }
}

fragment _b.java

public class fragment_b extends Fragment {
    // Log tag
    private static final String TAG = MovieFragment1.class.getSimpleName();

    // Movies json url
    private static final String url = "http://......";
    private ProgressDialog pDialog;
    private List<Movie> movieList = new ArrayList<Movie>();
    private ListView listView;
    private CustomListAdapter adapter;

    public MovieFragment1() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        hidePDialog();
    }

    private void hidePDialog() {
        if (pDialog != null) {
            pDialog.dismiss();
            pDialog = null;
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.activity_list, container, false);
        // Inflate the layout for this fragment

        final ListView listView = (ListView) rootView.findViewById(R.id.list);
        adapter = new CustomListAdapter(getActivity(), movieList);
        listView.setAdapter(adapter);

        pDialog = new ProgressDialog(getActivity());
        // Showing progress dialog before making http request
        pDialog.setMessage("Loading...");
        pDialog.show();


        // Creating volley request obj
        JsonArrayRequest movieReq = new JsonArrayRequest(url,
                new Response.Listener<JSONArray>() {
                    @Override
                    public void onResponse(JSONArray response) {
                        Log.d(TAG, response.toString());
                        hidePDialog();

                        // Parsing json
                        for (int i = 0; i < response.length(); i++) {
                            try {

                                JSONObject obj = response.getJSONObject(i);
                                Movie movie = new Movie();
                                if (obj.getString("tipe").equals("forearm")){
                                movie.setTitle(obj.getString("name"));
                                movie.setThumbnailUrl(obj.getString("images1"));
                                //movie.setDescribe(obj.getString("describe"));
                                //movie.setRating(((Number) obj.get("rating"))
                                //        .doubleValue());
                                movie.setYear(obj.getInt("id"));
                                movie.setTipe(obj.getString("tipe"));

                                /*// Genre is json array
                                JSONArray genreArry = obj.getJSONArray("genre");
                                ArrayList<String> genre = new ArrayList<String>();
                                for (int j = 0; j < genreArry.length(); j++) {
                                    genre.add((String) genreArry.get(j));
                                }
                                movie.setGenre(genre);*/

                                // adding movie to movies array
                                movieList.add(movie);
                            }
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }

                        }

                        // notifying list adapter about data changes
                        // so that it renders the list view with updated data
                        adapter.notifyDataSetChanged();
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                VolleyLog.d(TAG, "Error: " + error.getMessage());
                hidePDialog();

            }
        });

        // Adding request to request queue
        AppController.getInstance().addToRequestQueue(movieReq);

        return rootView;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
    }

    @Override
    public void onDetach() {
        super.onDetach();
    }
}

tabfragment.java( fragment 适配器)

public class TabFragment extends Fragment {

    public static TabLayout tabLayout;
    public static ViewPager viewPager;
    public static int int_items = 3 ;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        /**
         *Inflate tab_layout and setup Views.
         */
        View x =  inflater.inflate(R.layout.tab_layout,null);
        tabLayout = (TabLayout) x.findViewById(R.id.tabs);
        viewPager = (ViewPager) x.findViewById(R.id.viewpager);

        /**
         *Set an Apater for the View Pager
         */
        viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));

        /**
         * Now , this is a workaround ,
         * The setupWithViewPager dose't works without the runnable .
         * Maybe a Support Library Bug .
         */

        tabLayout.post(new Runnable() {
            @Override
            public void run() {
                tabLayout.setupWithViewPager(viewPager);
            }
        });

        return x;

    }

    class MyAdapter extends FragmentPagerAdapter{

        public MyAdapter(FragmentManager fm) {
            super(fm);
        }

        /**
         * Return fragment with respect to Position .
         */

        @Override
        public Fragment getItem(int position)
        {
            switch (position){
                case 0 : return new fragment_a();
                case 1 : return new HomeFragment();
                case 2 : return new fragment_b();
            }
            return null;
        }

        @Override
        public int getCount() {

            return int_items;

        }

        /**
         * This method returns the title of the tab according to the position.
         */

        @Override
        public CharSequence getPageTitle(int position) {

            switch (position){
                case 0 :
                    return "Chest";
                case 1 :
                    return "Movie";
                case 2 :
                    return "Forearm";
            }
            return null;
        }
    }

}

Answer 1

只需用

包裹你的 movieRequest

if(movieList.isEmpty()){
    JsonArrayRequest movieReq = new JsonArrayRequest(url, ... ETC...
    // etc
}

但请记住，使用这种方法，如果服务器上的数据发生更改，您的数据将不会更新，要使其可更新，您必须在每次填充之前清除 movieList:

movieList.clear();