android - 避免在 Pager Sliding Tab 中加载所有 fragment

Question

我在 PagerSlidingTab 中有几个 fragment 。因为一次性加载所有 fragment ，它没有良好的性能和质量(有时加载正确，有时转到 Volley onResponseError )。

在 fragment 中，我加载 json 数据并使用 Json 数据填充 RecyclerView。

One of my fragment :

public class Fragment_four extends Fragment {
    private boolean isFragmentLoaded = false;
    private static final String FIRST_URL = "http://myapiservice.com/api/3";
    private ProgressBar loadingProgressBar;
    private ArrayList<ModelDars> darsha = new ArrayList<ModelDars>();
    private RecyclerView reyclerCharDab;
    private AdapterRecyclerDars adapterRecyclerDars;
    private String after_url;

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

        //======================================
        loadingProgressBar = (ProgressBar) view.findViewById(R.id.prg_loading_frg_four);

        //recyclerview init
        reyclerCharDab = (RecyclerView) view.findViewById(R.id.recycler_frg_chaharom_dab);
        reyclerCharDab.setHasFixedSize(true);
        GridLayoutManager gridLayoutManager = new GridLayoutManager(getActivity(), 3);
        reyclerCharDab.setLayoutManager(gridLayoutManager);
        adapterRecyclerDars = new AdapterRecyclerDars(darsha, getActivity(), FIRST_URL, getActivity());
        reyclerCharDab.setAdapter(adapterRecyclerDars);

        if (helpers.isOnline(getActivity())) {
            //creating volley object request
            JsonObjectRequest request = new JsonObjectRequest(FIRST_URL, new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    if (response != null || response.length() > 0) {
                        try {
                            JSONArray data = response.getJSONArray("data");
                            for (int i = 0; i < data.length(); i++) {
                                JSONObject currentData = data.getJSONObject(i);
                                ModelDars newModelDars = new ModelDars();

                                newModelDars.setDarsId(currentData.getString("id"));
                                newModelDars.setDarsTitle(currentData.getString("title"));
                                newModelDars.setDarsPoster(currentData.getString("poster"));
                                newModelDars.setDarsVisitCnt(currentData.getString("visitcnt"));
                                newModelDars.setDarsDate(currentData.getString("date"));
                                newModelDars.setDarsCatId(currentData.getString("cat_id"));
                                newModelDars.setDarsCatName(currentData.getString("cat_name"));

                                darsha.add(newModelDars);
                            }
                            after_url = response.getString("pagination");

                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                        //notify adapter about data changed
                        adapterRecyclerDars.notifyDataSetChanged();
                        loadingProgressBar.setVisibility(View.GONE);
                    }
                }
            }, new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    loadingProgressBar.setVisibility(View.GONE);
                    Toast.makeText(getActivity(), "failed to fetch data from internet ", Toast.LENGTH_SHORT).show();
                }
            });
            AppController.getInstance().addToRequestQueue(request);

            // LOAD MORE FUNCTION =====================================================================

            reyclerCharDab.addOnScrollListener(new EndlessRecyclerViewScrollListener(gridLayoutManager) {
                @Override
                public void onLoadMore(int page, int totalItemsCount) {
                    if (after_url == "null") {

                    } else {

                        JsonObjectRequest request = new JsonObjectRequest(after_url, new Response.Listener<JSONObject>() {
                            @Override
                            public void onResponse(JSONObject response) {
                                if (response != null || response.length() > 0) {

                                    try {
                                        JSONArray data = response.getJSONArray("data");
                                        for (int i = 0; i < data.length(); i++) {
                                            JSONObject currentData = data.getJSONObject(i);
                                            ModelDars newModelDars = new ModelDars();

                                            newModelDars.setDarsId(currentData.getString("id"));
                                            newModelDars.setDarsTitle(currentData.getString("title"));
                                            newModelDars.setDarsPoster(currentData.getString("poster"));
                                            newModelDars.setDarsVisitCnt(currentData.getString("visitcnt"));
                                            newModelDars.setDarsDate(currentData.getString("date"));
                                            newModelDars.setDarsCatId(currentData.getString("cat_id"));
                                            newModelDars.setDarsCatName(currentData.getString("cat_name"));

                                            darsha.add(newModelDars);
                                        }
                                        after_url = response.getString("pagination");


                                    } catch (JSONException e) {
                                        e.printStackTrace();
                                    }
                                    //notify adapter about data changed
                                    adapterRecyclerDars.notifyDataSetChanged();

                                }
                            }
                        }, new Response.ErrorListener() {
                            @Override
                            public void onErrorResponse(VolleyError error) {

                            }
                        });
                        AppController.getInstance().addToRequestQueue(request);
                    }
                }
            });
        } else {
            Toast.makeText(getActivity(), "You dont have internet !", Toast.LENGTH_SHORT).show();
            loadingProgressBar.setVisibility(View.GONE);
        }
        return view;
    }
}

And This is the view pager adapter :

public class MainActivityPagerAdapter extends FragmentStatePagerAdapter {
    //============================================ Constructor
    public MainActivityPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    //============================================ GetItem Method ()
    @Override
    public Fragment getItem(int position) {
        Fragment frag = null;
        switch (position) {
            case 0:
                frag = new Fragment_one();
                break;
            case 1:
                frag = new Fragment_two();
                break;
            case 2:
                frag = new Fragment_three();
                break;
            case 3:
                frag = new Fragment_four();
                break;
        }
        return frag;
    }
    //============================================= GetCount Method ()
    @Override
    public int getCount() {
        return 4;
    }
    //============================================= GetPageTitle
    @Override
    public CharSequence getPageTitle(int position) {
        String title = "";
        switch (position) {
            case 0:
                title = "one";
                break;
            case 1:
                title = "two";
                break;
            case 2:
                title = "three";
                break;
            case 3:
                title = "four";
                break;
        }
        return title;
    }
}

Answer 1

根据您的评论，这里有一个只实例化 fragment 一次的 fragment ，并且只返回要显示的 fragment :

public class MainActivityPagerAdapter extends FragmentStatePagerAdapter {
private Fragment_one fragment_one;
private Fragment_two fragment_two;
private Fragment_three fragment_three;
private Fragment_four fragment_four;

//============================================ Constructor
public MainActivityPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.your_layout);
    fragment_one = new Fragment_one();
    fragment_two = new Fragment_two();
    fragment_three = new Fragment_three();
    fragment_four = new Fragment_four();
}

//============================================ GetItem Method ()
@Override
public Fragment getItem(int position) {
    switch (position) {
        case 0:
            return (fragment_one);
        case 1:
            return (fragment_two);
        case 2:
            return (fragment_three);
        case 3:
        default:
            return (fragment_four);
    }
}
}