如何重复十二次更新同一片段实例

Question

我正在使用可观察的模式来更新我的12个UpcomingGamesFragment片段

这是我的UpcomingGamesFragment类，其中包含我调用的更新方法

public class UpcomingGamesFragment extends Fragment implements Observer {

public void loadReleaseData(final int refresh) {
    if (mDatabaseLoading == null) {
        Log.d(TAG, "Fragment filter " + mFilter + " [fragment is null]");
        return;
    } else {
        Log.d(TAG, "Updating fragment: " + mFilter);
    }

    if (AppUtil.doesInternetWork(getActivity())) {
        // Viewpager does not load all fragments in memory, contents will be null
        mDatabaseLoading.setVisibility(View.VISIBLE);
        mUpcomingList.setVisibility(View.VISIBLE);
        mEmptyTextInfo.setVisibility(View.GONE);
        noInternetTxt.setVisibility(View.GONE);
        mUpcomingPageLayout.setClickable(false);

        Query query = mDatabaseRef.child("releases")
                .child(mRegion)
                .child("data")
                .orderByChild("m_y")
                .equalTo(mFilter);

        if (mFilter.equals("future")) {
            // Get all future releases
            Calendar calendar = Calendar.getInstance();
            calendar.set(Calendar.MONTH, Calendar.getInstance().get(Calendar.MONTH));
            calendar.set(Calendar.YEAR, Calendar.getInstance().get(Calendar.YEAR) + 1);
            query = mDatabaseRef.child("releases")
                    .child(mRegion)
                    .child("data")
                    .orderByChild("date")
                    .startAt(calendar.getTimeInMillis());
        }

        query.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.hasChildren()) {
                    if (refresh == 1) {
                        // Toast.makeText(getContext(), "adasfsdz", Toast.LENGTH_SHORT).show();
                        resetList();
                        Toast.makeText(getContext(), "Refreshing list...", Toast.LENGTH_SHORT).show();
                    }
                    for (DataSnapshot data : dataSnapshot.getChildren()) {
                        _Release release = data.getValue(_Release.class);
                        if (release != null) {
                            if (mSelectedPlatforms.isEmpty()) {
                                // No platform filter set add all releases!
                                if (release.getGame() != null) {
                                    mUpcomingReleases.add(release);
                                }
                            } else {
                                if (release.getGame() != null) {
                                    // If current platform is in ours shared pref of platforms
                                    if (!Collections.disjoint(release.getPlatform(), mSelectedPlatforms)) {
                                        mUpcomingReleases.add(release);
                                    }
                                }
                            }
                        }
                        mUpcomingGamesAdapter.notifyDataSetChanged();
                    }
                    // Check if list empty, if it is no releases matching platforms filter
                    if (mUpcomingReleases.isEmpty()) {
                        mEmptyTextInfo.setText("No releases found matching your platforms");
                        mEmptyTextInfo.setVisibility(View.VISIBLE);
                    }
                } else {
                    mEmptyTextInfo.setText("No releases found for this month");
                    mEmptyTextInfo.setVisibility(View.VISIBLE);
                }
                mDatabaseLoading.setVisibility(View.GONE);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                mDatabaseLoading.setVisibility(View.GONE);
            }
        });
    }
}

@Override
public void update() {
    loadReleaseData(0);
}
}

我还有另一个片段UpcomingViewPagerFragment，其中包含viewpager，其中包含12个片段，这个片段是可观察到的，这里是：

public class UpcomingViewPagerFragment extends Fragment implements Observable {
 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_upcoming_view_pager, container, false);
    // Viewpager
    mViewPager = view.findViewById(R.id.pager);
    mViewPager.setOffscreenPageLimit(3);
    // Get TabLayout from Main
    TabLayout tabLayout = ((MainActivity)getActivity()).mTabLayout;
    tabLayout.setupWithViewPager(mViewPager);
    mSectionsPagerAdapter = new SectionsPagerAdapter(getActivity().getSupportFragmentManager());
    Calendar calendar = Calendar.getInstance();
    SimpleDateFormat monthFormatter = new SimpleDateFormat("MMMM");
    // Add 11 months [Maximum] to show the releases for the next year [14 fragments in total]
    // First page recently released [-1] gets the last month of the current month
    calendar.add(Calendar.MONTH, -1);
    for (int i = 0; i < 14; i++) {
        String title = monthFormatter.format(calendar.getTime()) + " " + calendar.get(Calendar.YEAR);
        String queryId = (calendar.get(Calendar.MONTH) + 1) + "_" + calendar.get(Calendar.YEAR);
        if (i == 13) {
            // the last one
            queryId = "future";
            title = "Near future";
        }
        UpcomingGamesFragment upcomingGamesFragment = new UpcomingGamesFragment();
        mSectionsPagerAdapter.addFragment(upcomingGamesFragment, title, queryId);
        calendar.add(Calendar.MONTH, 1);
        // Log.d(TAG, "Added fragment: " + title + " : " + queryId);
        // Adding observers
        this.addObserver(upcomingGamesFragment);
    }
    mViewPager.setAdapter(mSectionsPagerAdapter);
    // Because the first page will always be the recently released
    mViewPager.setCurrentItem(1, true);
    return view;
}

@Override
public void addObserver(Observer o) {
    mObserversList.add(o);
}

@Override
public void deleteObserver(Observer o) {
    mObserversList.remove(o);
}

@Override
public void notifyObservers() {
    for (Observer observer: mObserversList) {
        observer.update();
    }
}
}

为清晰起见，省略了一些代码，例如两个片段的默认构造函数

然后，当我调用更新notifyObervers()中所有12个片段MainActivity的方法时，我总是得到组件mDatabaseLoading是null（请参阅{{1 }}方法），这样可见的片段就不会得到更新，知道为什么组件总是总是loadReleasData()吗？