How to get the Activity in nested fragments?

Question

I'm trying to get the activity calling getActivity() in the fragments contained in a ViewPager and this ViewPager is contained inside a Fragment. I need to call some methods from this activity in those fragments but the getActivity is always returning NULL for this fragments.

I don't know if this is a good approach but I need the fragments contained by the view pager to update their contents based on action bar actions and display messages saying is done or there was an error.

Help with this would be greatly appreciated.

Here is the code:

Internal Fragment:

    public class ReportSessionsFragment extends ReportPageFragment implements IUpdateView {

    private static final String TAG = ReportSessionsFragment.class.getSimpleName();

    private Sessions fSessions;

    private List<Report> reportList = null;
    private ReportsAdapter adapter = null;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return super.onCreateView(inflater, container, savedInstanceState);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        settings = ((BaseActivity)getActivity()).settings;
    }

    @Override
    public void onStart() {
        super.onStart();
        setCounter(db.getSessionsCount());

        if(settings.getSelectedRoom() != null){
            reportList = db.getSessionsByRoom(settings.getSelectedRoom().getName(),
                    settings.getStatusSelectedList());
            adapter = new ReportsAdapter(getActivity(), reportList, EReport.Sessions);
            mRecyclerView.setAdapter(adapter);
        }

    }

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

    @Override
    public void reload() {
        HashMap<String, Object> parameters = new HashMap<>();
        parameters.put(Fetcher.REQUEST_PARAMETERS, getEventInformation());

        showProgress(getString(R.string.txt_requesting_sessions));
        fSessions = new Sessions(getActivity(), this);
        fSessions.handleSession(parameters, false);
    }

    @Override
    public void delta() {

    }

    @Override
    public void updateProcess(String message) {

    }

    @Override
    public void onProcessEnded(RequestType type, boolean isProvisioningCompleted, String message) {
        reportList = db.getSessionsByRoom(settings.getSelectedRoom().getName(),
                settings.getStatusSelectedList());
        adapter.notifyDataSetChanged();
        hideProgress();
    }

    @Override
    public void onError(Exception e, boolean isProvisioningCompleted) {
        hideProgress();
        showError(getString(R.string.txt_error_title),
                e.getMessage());
    }
}

Fragment containing the ViewPager:

    public class ReportSessionsFragment extends ReportPageFragment implements IUpdateView {

    private static final String TAG = ReportSessionsFragment.class.getSimpleName();

    private Sessions fSessions;

    private List<Report> reportList = null;
    private ReportsAdapter adapter = null;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return super.onCreateView(inflater, container, savedInstanceState);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        settings = ((BaseActivity)getActivity()).settings;
    }

    @Override
    public void onStart() {
        super.onStart();
        setCounter(db.getSessionsCount());

        if(settings.getSelectedRoom() != null){
            reportList = db.getSessionsByRoom(settings.getSelectedRoom().getName(),
                    settings.getStatusSelectedList());
            adapter = new ReportsAdapter(getActivity(), reportList, EReport.Sessions);
            mRecyclerView.setAdapter(adapter);
        }

    }

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

    @Override
    public void reload() {
        HashMap<String, Object> parameters = new HashMap<>();
        parameters.put(Fetcher.REQUEST_PARAMETERS, getEventInformation());

        showProgress(getString(R.string.txt_requesting_sessions));
        fSessions = new Sessions(getActivity(), this);
        fSessions.handleSession(parameters, false);
    }

    @Override
    public void delta() {

    }

    @Override
    public void updateProcess(String message) {

    }

    @Override
    public void onProcessEnded(RequestType type, boolean isProvisioningCompleted, String message) {
        reportList = db.getSessionsByRoom(settings.getSelectedRoom().getName(),
                settings.getStatusSelectedList());
        adapter.notifyDataSetChanged();
        hideProgress();
    }

    @Override
    public void onError(Exception e, boolean isProvisioningCompleted) {
        hideProgress();
        showError(getString(R.string.txt_error_title),
                e.getMessage());
    }
}

The Activity:

    public class ReportsActivity extends BaseActivity implements IReports {

    private static final String TAG = ReportsActivity.class.getSimpleName();

    private ReportsFragment reportFragment;
    private HashMap<Integer, MenuItem> menuReports;

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

        reportFragment = new ReportsFragment();
        addFragment(reportFragment);
    }

    @Override
    protected void onStart() {
        super.onStart();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_reports, menu);

        menuReports = new HashMap<>();

        for(int index = 0; index < menu.size(); index++ ){
            MenuItem mi = menu.getItem(index);
            menuReports.put(mi.getItemId(), mi);
        }

        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        ReportPageFragment reportPage = (ReportPageFragment)reportFragment.getCurrentReportPage();

        switch (item.getItemId()){
            case R.id.action_reload:
                reportPage.reload();
                break;
            case R.id.action_delta:
                reportPage.delta();
                break;
        }

        return true;
    }

    @Override
    public void displayOptionsByReport(int position) {
        MenuItem miReload = null;
        if(menuReports != null){
             miReload = (MenuItem) menuReports.get(R.id.action_reload);
        }

        switch (position){
            case REPORT_SESSION:
                miReload.setVisible(true);
                break;
            case REPORT_ENROLLMENT:
                miReload.setVisible(true);
                break;
            case REPORT_REGISTRANTS:
                miReload.setVisible(false);
                break;
            case REPORT_ASSOCIATIONS:
                miReload.setVisible(false);
                break;
        }
    }
}

FragmentPagerAdapter:

public class ReportsPagerAdapter extends FragmentStatePagerAdapter {

private Context ctx;

public ReportsPagerAdapter(Context ctx, FragmentManager fm) {
    super(fm);
    this.ctx = ctx;
}

@Override
public Fragment getItem(int position) {
    Fragment fragment = null;

    switch (position){
        case 0:
            fragment = Fragment.instantiate(ctx, ReportSessionsFragment.class.getName());
            break;
        case 1:
            fragment = Fragment.instantiate(ctx, ReportEnrollmentFragment.class.getName());
            break;
        case 2:
            fragment = Fragment.instantiate(ctx, ReportRegistrantsFragment.class.getName());
            break;
        case 3:
            fragment = Fragment.instantiate(ctx, ReportAssociationsFragment.class.getName());
            break;
    }

    return fragment;
}

@Override
public int getCount() {
    String[] reportListNames = ctx.getResources().getStringArray(R.array.reports);
    return reportListNames.length;
}

@Override
public CharSequence getPageTitle(int position) {
    String[] reportListNames = ctx.getResources().getStringArray(R.array.reports);
    return reportListNames[position];
}
}

Answer 1

Every fragment, even those that are childen of another fragment, receive a call to onAttach() when they are added to the fragment tree. The activity containing the fragment is passed in as a parameter. The simplest solution is may be to save the activity as a member of your fragment. Then it is available when needed later.

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    //save the activity to a member of this fragment
    mHostActivity = activity;
}

An alternative, for a fragment that is always at a fixed depth in the tree, is to use getParent() as many times as needed to get to the top-most fragment. For example, in your fragments that are children of the pager fragment:

getParentFragment().getActivity()