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Wait for event when fragments fully initialized in FragmentPagerAdapter to setup them with data

I have an activity with collapsing AppBarLayout. In onCreate() method I am sending request to server to get some data. And depending what data I get - I need to dynamically in runtime choose what view to show to the user: 1. MyFragment1; or 2. TabLayout/ViewPager with FragmentPagerAdapter, which has two fragments in it. And I need to set some data to that fragments. But the issue is in next: I already have data and set it to fragments in my adapter, but fragment method onCreate is not yet called, and my layout is not initialized. That's how I get crash on populating data into layout view. So, how can I make somehow - fragment created and initialized it's fields first and only then setup it with data? Thanks.
private MenuFragment1 menu1Fragment1;
private MenuFragment3 menu1Fragment3;
private TabMenuAdapter adapter;
private void setupViewPager(ViewPager viewPager) {
menu1Fragment1 = new MenuFragment1();
menu1Fragment3 = new MenuFragment3();
adapter = new TabMenuAdapter(getSupportFragmentManager());
adapter.addFragment(menu1Fragment1, "Menu 1");
adapter.addFragment(menu1Fragment3, "Menu 2");
viewPager.setAdapter(adapter);
}
public onDataLoaded(String data)
{
//at this point, fragment is created, but it's View fields are NULL!!
menu1Fragment1.data = data;
}
#Layout(id = R.layout.content_shop_final)
public class ShopFinalTermsFragment extends BaseFragment {
private static final String SANS_SERIF_FAMILY_NAME = "sans-serif";
private static final String SANS_SERIF_MEDIUM_FAMILY_NAME = "sans-serif-medium";
private InfoModel InfoModel;
private RateModel RateModel;
#BindView(R.id.shop_final_nested_scroll_view)
NestedScrollView nestedScrollView;
#BindView(R.id.shop_final_pending_txt)
TextView pendingDurationTxt;
#BindView(R.id.shop_final_rate_cond_rv)
RecyclerView rateCondRv;
#BindView(R.id.shop_final_description_txt)
TextView descriptionTxt;
#Inject
ToolsManager toolsManager;
RateConditionsAdapter adapter;
private String getParams;
public static ShopFinalTermsFragment newInstance(String getParams, InfoModel shopInfoModel, RateModel RateModel) {
ShopFinalTermsFragment fragment = new ShopFinalTermsFragment();
Bundle args = new Bundle();
args.putString(SHOP_GET_PARAMS, shopGetParams);
args.putSerializable(INFO_MODEL_KEY, shopInfoModel);
args.putSerializable(MODEL_KEY, userCashbackRateModel);
fragment.setArguments(args);
return fragment;
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
this.GetParams = getArguments().getString(SHOP_GET_PARAMS);
this.InfoModel = (InfoModel) getArguments().getSerializable(INFO_MODEL_KEY);
this.RateModel = (RateModel) getArguments().getSerializable(RATE_MODEL_KEY);
}
}
#Override
protected void setupInOnCreateView() {
nestedScrollView.setVisibility(View.VISIBLE);
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
conditionsTxt.setTypeface(Typeface.create(SANS_SERIF_FAMILY_NAME, Typeface.BOLD));
} else {
conditionsTxt.setTypeface(Typeface.create(SANS_SERIF_MEDIUM_FAMILY_NAME, Typeface.NORMAL));
}
}
#Override
protected void inject() {
ShopsComponent shopsComponent = DaggerShopsComponent.builder()
.applicationComponent(((BaseActivity) getActivity()).getApplicationComponent())
.build();
shopsComponent.inject(this);
}
public void setupWithData(InfoModel InfoModel, RateModel RateModel) {
//THIS METHOD IS COLLED FROM ACTIVITY'S onDataLoaded(InfoModel InfoModel, RateModel RateModel) method
setupShopInformation(shopInfoModel);
setCashBackRateModel(userCashbackRateModel);
}
}

You are using the dependency in a wrong way. It's not the activity that should call setupWithData on a fragment but it should be a fragment getting data from the activity (or other storage) instead. This way you will break this dependency on the fragment lifecycle which ends up being uninitialized.
Get the data from the server, store it where you need to, and update the UI from your activity. At this point you either show MyFragment1 or your TabLayout/ViewPager. If it's a TabLayout or a ViewPager, all you do is creating fragments and adding the to the layout or a corresponding pager adapter. That's it. You don't set the data at this point.
Now when your inner fragments populate in the pager adapter, they will go through onAttach, onCreate, onStart and onResume lifecycle methods. onResume is a good place to load the data. You either access it directly from the fragment, or get it from your outbound activity - depends on what makes more sense for you. If you need an activity reference, you can access it via getActivity() method in the fragment.
So in the fragment's onResume you will have something like:
setupShopInformation((YourActivity) getActivity()).getShopInfoModel());
setCashBackRateModel((YourActivity) getActivity()).getUserCashbackRateModel());
Although it would be even better to have it stored in some state class. But that will be a separate question.
Good luck!

Why getContext() in fragment sometimes returns null?

Why getContext() sometimes returns null? I pass context to LastNewsRVAdapter.java as an argument. But LayoutInflater.from(context) sometimes crashes. I'm getting a few crash reports on play console. Below is crash report.
java.lang.NullPointerException
com.example.adapters.LastNewsRVAdapter.<init>
java.lang.NullPointerException:
at android.view.LayoutInflater.from (LayoutInflater.java:211)
at com.example.adapters.LastNewsRVAdapter.<init> (LastNewsRVAdapter.java)
at com.example.fragments.MainFragment$2.onFailure (MainFragment.java)
or .onResponse (MainFragment.java)
at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run
(ExecutorCallAdapterFactory.java)
at android.os.Handler.handleCallback (Handler.java:808)
at android.os.Handler.dispatchMessage (Handler.java:103)
at android.os.Looper.loop (Looper.java:193)
at android.app.ActivityThread.main (ActivityThread.java:5299)
at java.lang.reflect.Method.invokeNative (Method.java)
at java.lang.reflect.Method.invoke (Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run
(ZygoteInit.java:825)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:641)
at dalvik.system.NativeStart.main (NativeStart.java)
This is LastNewsRVAdapter.java constructor.
public LastNewsRVAdapter(Context context, List<LatestNewsData>
latestNewsDataList, FirstPageSideBanner sideBanner) {
this.context = context;
this.latestNewsDataList = latestNewsDataList;
inflater = LayoutInflater.from(context);
this.sideBanner = sideBanner;
}
This is the code onCreateView inside Fragment
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
final View view = inflater.inflate(R.layout.fragment_main_sonku_kabar, container, false);
tvSonkuKabar = view.findViewById(R.id.textview_sonku_kabar_main);
tvNegizgiKabar = view.findViewById(R.id.textview_negizgi_kabar_main);
refresh(view);
final SwipeRefreshLayout swipeRefreshLayout = (SwipeRefreshLayout) view.findViewById(R.id.mainRefreshSonkuKabar);
swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
#Override
public void onRefresh() {
refresh(view);
swipeRefreshLayout.setRefreshing(false);
}
});
setHasOptionsMenu(true);
return view;
}
This is refresh method inside Fragment
private void refresh(final View view) {
sideBanner = new FirstPageSideBanner();
final RecyclerView rvLatestNews = (RecyclerView) view.findViewById(R.id.recViewLastNews);
rvLatestNews.setLayoutManager(new LinearLayoutManager(getContext(), LinearLayoutManager.VERTICAL, false));
rvLatestNews.setNestedScrollingEnabled(false);
App.getApiService().getLatestNews().enqueue(new Callback<LatestNews>() {
#Override
public void onResponse(Call<LatestNews> call, Response<LatestNews> response) {
if (response.isSuccessful() && response.body().isSuccessfull()){
adapter = new LastNewsRVAdapter(getContext(), response.body().getData(), sideBanner);
rvLatestNews.setAdapter(adapter);
tvSonkuKabar.setVisibility(View.VISIBLE);
}
}
#Override
public void onFailure(Call<LatestNews> call, Throwable t) {
}
});

As the accepted answer says, you must look into the way you are using and caching context. Somehow you are leaking context that is causing Null Pointer Exception.
Below Answer is as per the first revision of the question.
Use onAttach() to get Context. Most of the cases, you don't need this solution so use this solution only if any other solution does not work. And you may create a chance to activity leak, so be cleaver while using it. You may require to make context null again when you leave from fragment
// Declare Context variable at class level in Fragment
private Context mContext;
// Initialise it from onAttach()
#Override
public void onAttach(Context context) {
super.onAttach(context);
mContext = context;
}
This context will be available in onCreateView, so You should use it.
From Fragment Documentation
Caution: If you need a Context object within your Fragment, you can call getContext(). However, be careful to call getContext() only
when the fragment is attached to an activity. When the fragment is not
yet attached, or was detached during the end of its lifecycle,
getContext() will return null.

First of all, as you can see on this link, the method onCreateView() inside the fragment's lifecycle comes after onAttach(), so you should have already a context at that point. You may wonder, why does getContext() return null then? the problem lies on where you are creating your adapter:
App.getApiService().getLatestNews().enqueue(new Callback<LatestNews>() {
#Override
public void onResponse(Call<LatestNews> call, Response<LatestNews> response) {
if (response.isSuccessful() && response.body().isSuccessfull()){
adapter = new LastNewsRVAdapter(getContext(), response.body().getData(), sideBanner);
rvLatestNews.setAdapter(adapter);
tvSonkuKabar.setVisibility(View.VISIBLE);
}
}
#Override
public void onFailure(Call<LatestNews> call, Throwable t) {
}
});
Though you are specifying a callback in onCreateView(), that does not mean the code inside that callback will run at that point. It will run and create the adapter after the network call is done. With that in mind, your callback may run after that point in the lifecycle of the fragment. What I mean is that the user can enter that screen (fragment) and go to another fragment or return to the previous one before the network request finishes (and the callback runs). If that happens, then getContext() could return null if the user leaves the fragment (onDetach() may have been called).
Besides, you can have memory leaks also, in case the activity is destroyed before your network request finishes. So you have two issues there.
My suggestions to solve those issues are:
in order to avoid the null pointer exception and the memory leak, you should cancel the network request when the onDestroyView() inside the fragment is being called (retrofit returns an object that can cancel the request: link).
Another option that will prevent the null pointer exception is to move the creation of the adapter LastNewsRVAdapter outside the callback and keep a reference to it in the fragment. Then, use that reference inside the callback to update the content of the adapter: link

So getContext() is not called in onCreateView(). It's called inside the onResponse() callback which can be invoked anytime. If it's invoked when your fragment is not attached to activity, getContext() will return null.
The ideal solution here is to Cancel the request when the activity/fragment is not active (like user pressed back button, or minimized the app).
Another solution is to simply ignore whatever is in onResponse() when your fragment is not attached to your activity, like this: https://stackoverflow.com/a/10941410/4747587

When you are sure fragment is attached to its host(onResume, onViewCreated, etc) use this instead of getContext() :
requireContext()
It will not be inspected by lint, but it will throw an Exception if context detached!
Then you should check nullity by if clouse (or some thing) or be sure that if the program reaches this line, it isn't null.
In retrofit calls or retrofit (and may others in the same way), it will return a disposable that must be cleared or disposed before onDestroy.

Write a common method that will ensure you will never get null Context.
public class BaseFragment extends Fragment {
private Context contextNullSafe;
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
/*View creation related to this fragment is finished here. So in case if contextNullSafe is null
* then we can populate it here.In some discussion in - https://stackoverflow.com/questions/6215239/getactivity-returns-null-in-fragment-function
* and https://stackoverflow.com/questions/47987649/why-getcontext-in-fragment-sometimes-returns-null,
* there are some recommendations to call getContext() or getActivity() after onCreateView() and
* onViewCreated() is called after the onCreateView() call every time */
if (contextNullSafe == null) getContextNullSafety();
}
#Override
public void onAttach(#NonNull Context context) {
super.onAttach(context);
contextNullSafe = context;
}
/**CALL THIS IF YOU NEED CONTEXT*/
public Context getContextNullSafety() {
if (getContext() != null) return getContext();
if (getActivity() != null) return getActivity();
if (contextNullSafe != null) return contextNullSafe;
if (getView() != null && getView().getContext() != null) return getView().getContext();
if (requireContext() != null) return requireContext();
if (requireActivity() != null) return requireActivity();
if (requireView() != null && requireView().getContext() != null)
return requireView().getContext();
return null;
}
/**CALL THIS IF YOU NEED ACTIVITY*/
public FragmentActivity getActivityNullSafety() {
if (getContextNullSafety() != null && getContextNullSafety() instanceof FragmentActivity) {
/*It is observed that if context it not null then it will be
* the related host/container activity always*/
return (FragmentActivity) getContextNullSafety();
}
return null;
}

How can I populate fragments with data that aren't available until after the fragment's creation?

I have an activity that grabs data via WebService, from there it creates elements to display the data. Some data is grouped so my solution was to display the grouped data in their own fragments below the main layout, allowing the user to swipe across the groups, probably with a tabs at the top to show the group name.
The problem I came across was that the fragments in the activity are created before that web call takes place, making them empty or using old data. I then created a sharedpreferences listener and placed the fragments layout creation method within it. The main method grabs the data, writes to sharedpreferences the fragment detects the change and creates it's layout, Or so I thought.
Some groups are the same between items, so moving from one to the other won't trigger that onchange event thus not triggering the layout creation method. I then decided to do the following to always trigger the onchange event after the sharedpreferences are written
final Boolean updated = settings.getBoolean("UPDATED_1", false);
SharedPreferences.Editor editor = settings.edit();
editor.putBoolean("UPDATED_" + pageNum, !updated);
I just don't think that's the best solution, it also has it's problems and isn't triggering every time (Which I have yet to troubleshoot)
What's a better solution for all this? I also have a memory leak I haven't diagnosed yet to make things even more of a headache.
I've just thought of moving my data grabbing method to before the ViewPager initialization but I'm not yet sure if this will solve my problem.

I would not recommend waiting until you get the data to show the view as it will affect the User Experience and look sluggish.
Instead, you could implement an AsyncTaskLoader in your fragment so you can inform the Fragment's View with a BroadcastReceiver once you get the data from your server. In the meantime, just show a spinner until the data are retrieved, then you hide it and update your list with a adapter.notifyDataSetChanged();.
Here is an example of a AsyncTaskLoader (In my case it's a database query instead of a server call like you):
public class GenericLoader<T extends Comparable<T>> extends AsyncTaskLoader<ArrayList<T>> {
private Class clazz;
public GenericLoader(Context context, Class<T> clazz) {
super(context);
this.clazz = clazz;
}
#Override
public ArrayList<T> loadInBackground() {
ArrayList<T> data = new ArrayList<>();
data.addAll(GenericDAO.getInstance(clazz).queryForAll());
Collections.sort(data);
return data;
}
}
Then in your Fragment:
public class FragmentMobileData extends Fragment implements ListAdapter.OnItemClickListener, LoaderManager.LoaderCallbacks<ArrayList<EntityCategories.EntityCategory>> {
public static String TAG = "FragmentMobileData";
private ImageListAdapter adapter;
private ArrayList<EntityList> mCategories = new ArrayList<>();
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
Bundle bundle = intent.getExtras();
String result = bundle.getString(DatabaseService.RESULT);
if (DatabaseService.NO_CONNECTION.equals(result)) {
Utils.showToastMessage(getActivity(), "No internet connexion", true);
} else if (DatabaseService.RESULT_TIMEOUT.equals(result)) {
Utils.showToastMessage(getActivity(), "Bad connection. Retry", true);
}
getActivity().getSupportLoaderManager().initLoader(1, null, FragmentMobileData.this).forceLoad();
}
};
#Bind(R.id.progressBarEcard)
ProgressBar spinner;
#Bind(R.id.list)
RecyclerView list;
public FragmentMobileData() {
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_mobile_plan, container, false);
ButterKnife.bind(this, view);
((AppCompatActivity) getActivity()).getSupportActionBar().setTitle("Mobile");
list.setLayoutManager(new LinearLayoutManager(context));
list.addItemDecoration(new DividerItemDecoration(context, R.drawable.divider));
adapter = new ImageListAdapter(mCategories, this);
list.setAdapter(adapter);
Intent intent = new Intent(context, DatabaseService.class);
intent.setAction(DatabaseService.UPDATE_DATA);
getActivity().startService(intent);
return view;
}
#Override
public void onPause() {
super.onPause();
getActivity().unregisterReceiver(mReceiver);
}
#Override
public void onResume() {
super.onResume();
getActivity().registerReceiver(mReceiver, new IntentFilter(DatabaseService.UPDATE_DATA));
}
#Override
public Loader<ArrayList<EntityCategories.EntityCategory>> onCreateLoader(int id, Bundle args) {
return new GenericLoader(context, EntityCategories.EntityCategory.class);
}
#Override
public void onLoadFinished(Loader<ArrayList<EntityCategories.EntityCategory>> loader, ArrayList<EntityCategories.EntityCategory> data) {
if (mCategories.size() != data.size()) {
mCategories.clear();
mCategories.addAll(data);
adapter.notifyDataSetChanged();
Intent intent = new Intent(context, DownloadFilesService.class);
context.startService(intent);
}
spinner.setVisibility(View.GONE);
}
#Override
public void onLoaderReset(Loader<ArrayList<EntityCategories.EntityCategory>> loader) {
mCategories.clear();
adapter.notifyDataSetChanged();
}
//...
}

Maybe I misunderstood something. But in your case I think there is pretty good alternative to create, for example, your fragment which will display some group of data, then in it's creation stage show progress bar in ui, and meantime do request to the data in background. Then handle result data and show it, and hide progress bar.
This can be achieved with implementing MVP pattern to provide flexibility of code and easy testing. Also you can use rxJava and Retrofit to handle requests in a convenient way. More information about MVP and samples you can find here.
If you don't want to provide this way for some reason. For example, you have undetermined number of groups, which you will receive in future somehow and you want to dynamically build your fragments base on data which you receive, then I suggest you can organize presentation layer in your activity. In this layer your will receive data then pass it to special handler, which will divide it to groups and base on them will ask activity to create fragment. In constructor you will send already received data (so it is need to implement Parcelable interface).

Where and how to do network call when using fragments

I am building an app that has fragments. Im not entirely sure when to make a http nw call to get data to populate components within these fragments. I have a call that gets all the data i need for all my fragments to draw the screen. I have tested that a async task gets that data ok but in the postExecute i don't have access to components unless im in the fragment class, even then how would i put it in there.
I can do a asyncTask and see my data coming back but where do i put this, i want to make the call once.
ActivityTileData.getLoginTileDataArray(getActivity()); currently returns dummy data, ideally this would do the network call.
public class StaggeredGridActivityFragment extends FragmentActivity {
private static final String TAG = "StaggeredGridActivityFragment";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE); //remove title bar
final FragmentManager fm = getSupportFragmentManager();
// Create the list fragment and add it as our sole content.
if (fm.findFragmentById(android.R.id.content) == null) {
final StaggeredGridFragment fragment = new StaggeredGridFragment();
fm.beginTransaction().add(android.R.id.content, fragment).commit();
}
}
private class StaggeredGridFragment extends Fragment implements
AbsListView.OnScrollListener, AbsListView.OnItemClickListener {
private StaggeredGridView mGridView;
private boolean mHasRequestedMore;
private TilesAdapter mAdapter;
private ArrayList<String> mData;
#Override
public void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
#Override
public View onCreateView(final LayoutInflater inflater, final ViewGroup container, final Bundle savedInstanceState) {
return inflater.inflate(R.layout.activity_sgv, container, false);
}
#Override
public void onActivityCreated(final Bundle savedInstanceState) {
//Encapsulate all within a post cereate from a async task or call a blocking http call
super.onActivityCreated(savedInstanceState);
mGridView = (StaggeredGridView) getView().findViewById(R.id.grid_view);
if (savedInstanceState == null) {
final LayoutInflater layoutInflater = getActivity().getLayoutInflater();
View header = layoutInflater.inflate(R.layout.list_item_header_footer, null);
mGridView.addHeaderView(header);
}
if (mAdapter == null) {
mAdapter = new TilesAdapter(getActivity(), R.id.summary1_value);
}
if (mData == null) {
mData = ActivityTileData.getLoginTileDataArray(getActivity());
}
for (String data : mData) {
mAdapter.add(data); //Add each mData TileAdapter element to an mAdapter where it will be further broken down and used by the TileAdapter
}
mGridView.setAdapter(mAdapter);
mGridView.setOnScrollListener(this);
mGridView.setOnItemClickListener(this);
}

I would recommend to do n/w call in onCreate of your activity and make sets of data for your each fragment and put them in arguments of fragment. You can load the data in newInstance of fragment by getting required data from bundle.I have done one project of this type and it worked for me.
Note: The above method works if the data doesn't need to change once it has been set.

Do not make the async call inside your fragments and/or activities. If you do, you will get many issues handling config changes (like when the user rotates the screen). For my experience, what I usually do is to create a class called Loader (not the Android framework Loader class, it is an overkill for this purpose) and place your AsyncTask or loader thread there. From your fragment/activity get a reference to that class that should be implemented as a singleton (override your Application class for this) on its onCreate(). Then, call loader.loadDate() whenever you need it. If you want to handle config changes, create an observable pattern in your Loader class, so fragments and activities can register to hear loading events such as loadFinished(data) or loadError(error). Also, if you dont want to query for data everytime a config change happens, set a catched variable inside your loader that holds the previous loaded data.

Fragment's reference to mActivity becomes null after orientation change. Ineffective fragment state maintenance

My application consists of several fragments. Up until now I've had references to them stored in a custom Application object, but I am beginning to think that I'm doing something wrong.
My problems started when I realized that all my fragment's references to mActivity becomes null after an orientation change. So when I call getActivity() after an orientation change, a NullPointerException is thrown.
I have checked that my fragment's onAttach() is called before I make the call to getActivity(), but it still returns null.
The following is a stripped version of my MainActivity, which is the only activity in my application.
public class MainActivity extends BaseActivity implements OnItemClickListener,
OnBackStackChangedListener, OnSlidingMenuActionListener {
private ListView mSlidingMenuListView;
private SlidingMenu mSlidingMenu;
private boolean mMenuFragmentVisible;
private boolean mContentFragmentVisible;
private boolean mQuickAccessFragmentVisible;
private FragmentManager mManager;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/*
* Boolean variables indicating which of the 3 fragment slots are visible at a given time
*/
mMenuFragmentVisible = findViewById(R.id.menuFragment) != null;
mContentFragmentVisible = findViewById(R.id.contentFragment) != null;
mQuickAccessFragmentVisible = findViewById(R.id.quickAccessFragment) != null;
if(!savedInstanceState != null) {
if(!mMenuFragmentVisible && mContentFragmentVisible) {
setupSlidingMenu(true);
} else if(mMenuFragmentVisible && mContentFragmentVisible) {
setupSlidingMenu(false);
}
return;
}
mManager = getSupportFragmentManager();
mManager.addOnBackStackChangedListener(this);
final FragmentTransaction ft = mManager.beginTransaction();
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
if (!mMenuFragmentVisible && mContentFragmentVisible) {
/*
* Only the content fragment is visible, will enable sliding menu
*/
setupSlidingMenu(true);
onToggle();
ft.replace(R.id.contentFragment, getCustomApplication().getSportsFragment(), SportsFragment.TAG);
} else if (mMenuFragmentVisible && mContentFragmentVisible) {
setupSlidingMenu(false);
/*
* Both menu and content fragments are visible
*/
ft.replace(R.id.menuFragment, getCustomApplication().getMenuFragment(), MenuFragment.TAG);
ft.replace(R.id.contentFragment, getCustomApplication().getSportsFragment(), SportsFragment.TAG);
}
if (mQuickAccessFragmentVisible) {
/*
* The quick access fragment is visible
*/
ft.replace(R.id.quickAccessFragment, getCustomApplication().getQuickAccessFragment());
}
ft.commit();
}
private void setupSlidingMenu(boolean enable) {
/*
* if enable is true, enable sliding menu, if false
* disable it
*/
}
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
// launch the fragment that was clicked from the menu
}
#Override
public void onBackPressed() {
// Will let the user press the back button when
// the sliding menu is open to display the content.
if (mSlidingMenu != null && mSlidingMenu.isMenuShowing()) {
onShowContent();
} else {
super.onBackPressed();
}
}
#Override
public void onBackStackChanged() {
/*
* Change selected position when the back stack changes
*/
if(mSlidingMenuListView != null) {
mSlidingMenuListView.setItemChecked(getCustomApplication().getSelectedPosition(), true);
}
}
#Override
public void onToggle() {
if (mSlidingMenu != null) {
mSlidingMenu.toggle();
}
}
#Override
public void onShowContent() {
if (mSlidingMenu != null) {
mSlidingMenu.showContent();
}
}
}
The following is a stripped version of the CustomApplication. My thoughts behind this implementation was to guarantee only one instance of each fragment throughout my application's life cycle.
public class CustomApplication extends Application {
private Fragment mSsportsFragment;
private Fragment mCarsFragment;
private Fragment mMusicFragment;
private Fragment mMoviesFragment;
public Fragment getSportsFragment() {
if(mSsportsFragment == null) {
mSsportsFragment = new SportsFragment();
}
return mSsportsFragment;
}
public Fragment getCarsFragment() {
if(mCarsFragment == null) {
mCarsFragment = new CarsFragment();
}
return mCarsFragment;
}
public Fragment getMusicFragment() {
if(mMusicFragment == null) {
mMusicFragment = new MusicFragment();
}
return mMusicFragment;
}
public Fragment getMoviesFragment() {
if(mMoviesFragment == null) {
mMoviesFragment = new MoviesFragment();
}
return mMoviesFragment;
}
}
I am very interested in tips on how to best implement multiple fragments and how to maintain their states. For your information, my applicaion consists of 15+ fragments so far.
I have done some research and it seems that FragmentManager.findFragmentByTag() is a good bet, but I haven't been able to successfully implement it.
My implementation seems to work good except for the fact that mActivity references become null after orientation changes, which lets me to believe that I may have some memory leak issues as well.
If you need to see more code, please let me know. I purposely avoided including fragment code as I strongly believe issues are related to my Activity and Application implementations, but I may be wrong.
Thanks for your time.

My thoughts behind this implementation was to guarantee only one instance of each fragment throughout my application's life cycle
This is probably part, if not all, of the source of your difficulty.
On a configuration change, Android will re-create your fragments by using the public zero-argument constructor to create a new instance. Hence, your global-scope fragments will not "guarantee only one instance of each fragment".
Please delete this custom Application class. Please allow the fragments to be re-created naturally, or if they need to live for the life of a single activity, use setRetainInstance(true). Do not attempt to reuse fragments across activities.

I don't see where are you using the reference to mActivity. But don't hold a reference to it. Always use getActivity since the Activity can be recreated after orientation change. Also, don't ever set the fragment's fields by setters or by assigning always use a Bundle and Arguments
Best practice for instantiating a new Android Fragment
Also you can use setRetainInstance(true) to keep all the fragment's members during orientation change.
Understanding Fragment's setRetainInstance(boolean)

To resolve this problem you have to use the activity object provided by onAttach method of fragment so when you change the orientation fragment is recreated so onAttach give you the current reference

you can use onAttach(Context context) to create a private context variable in fragment like this
#Override
public void onAttach(Context context) {
this.context = context;
super.onAttach(context);
}
on changing orientation, onAttach gives you new reference to the context, if you want reference to activity, you can typecast context to activity.

Context can also be reassigned inside onCreate in fragments as OnCreate is called when device is rotated
private Context mContext;
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//get new activity reference here
mContext = getActivity();
}
pass this mContext throughout the fragment

If you don't setRetainInstance(true) in onCreate ... the collection e.g List<Object>, Vector<Object> in Application class will get null. Make sure you setRetainInstance(true) to make them alive.