Handle backstack using Navigation Activity and BottomNavigationView at same time about fragnav HOT 2 CLOSED

@Override
    public void onBackPressed() {
        if (mCurrentIndex == INDEX_RECENTS && mDrawer != null && mDrawer.isDrawerOpen()) {
            mDrawer.closeDrawer();
        } else if (mNavController.getCurrentStack().size() > 1) {
            mNavController.popFragment();
        } else {
            super.onBackPressed();
        }
    }

@Override
   public Fragment getRootFragment(int i) {
    mCurrentIndex = i;
       switch (i) {
           case INDEX_RECENTS:
               return ExploreBaseFragment.newInstance(0); //this is fragment with BottomNavigationView having 3 child fragment
           case INDEX_FAVORITES:
               return MyUploadsFragment.newInstance(0);
           case INDEX_NEARBY:
               return CategoryFragment.newInstance(0);
       }
       throw new IllegalStateException("Need to send an index that we know");
   }

 if (mNavController.getCurrentStack().size() > 1) {
            mNavController.popFragment();
        }

public class MainActivity extends AppCompatActivity implements Drawer.OnDrawerItemClickListener, BaseFragment.FragmentNavigation, FragNavController.RootFragmentListener {

    private static final String TAG = "MainActivity";
    private final int INDEX_RECENTS = FragNavController.TAB1;
    private final int INDEX_FAVORITES = FragNavController.TAB2;
    private final int INDEX_NEARBY = FragNavController.TAB3;
    //save our header or mDrawer
    private AccountHeader mAccountHeader = null;
    private Drawer mDrawer = null;
    private FragNavController mNavController;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // set Toolbar
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        //create account header
        createAccountHeader(savedInstanceState);

        //Create the drawer
        createDrawer(savedInstanceState, toolbar, getDrawerItems());

        mNavController = new FragNavController(savedInstanceState, getSupportFragmentManager(), R.id.frame_container, this, 3, INDEX_RECENTS);

    }

    @Override
    public boolean onItemClick(View view, int position, IDrawerItem drawerItem) {
        Log.d(TAG, "onItemClick Position: " + position);
        if (drawerItem != null) {
            if (drawerItem.getIdentifier() == 100) {
                mNavController.switchTab(INDEX_RECENTS);
            } else if (drawerItem.getIdentifier() == 200) {
                mNavController.switchTab(INDEX_FAVORITES);
            } else if (drawerItem.getIdentifier() >= 0 && drawerItem.getIdentifier() <= 15) {
                mNavController.switchTab(INDEX_NEARBY);
            } else if (drawerItem.getIdentifier() == 500) {
                mNavController.showDialogFragment(new RatingFragment());
            } else if (drawerItem.getIdentifier() == 700) {
                mNavController.showDialogFragment(new SignOutFragment());
            } else if (drawerItem.getIdentifier() == 400) {
                startActivity(new Intent(MainActivity.this, SettingsActivity.class));
            }
        }
        return false;
    }

    @Override
    public void onBackPressed() {
        if (mDrawer != null && mDrawer.isDrawerOpen()) {
            mDrawer.closeDrawer();
        } else if (mNavController.getCurrentStack().size() > 1) {
            mNavController.popFragment();
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public void pushFragment(Fragment fragment) {
        mNavController.pushFragment(fragment);
    }

    @Override
    public Fragment getRootFragment(int i) {
        switch (i) {
            case INDEX_RECENTS:
                return ExploreBaseFragment.newInstance(0); //Fragment with three child fragment
            case INDEX_FAVORITES:
                return MyUploadsFragment.newInstance(0);
            case INDEX_NEARBY:
                return CategoryFragment.newInstance(0);
        }
        throw new IllegalStateException("Need to send an index that we know");
    }
}

public class ExploreBaseFragment extends BaseFragment implements BottomNavigationView.OnNavigationItemSelectedListener, FragNavController.RootFragmentListener {

    private final int INDEX_POPULAR = FragNavController.TAB1;
    private final int INDEX_EXPLORE = FragNavController.TAB2;
    private final int INDEX_FAVORITES = FragNavController.TAB3;
    private FragNavController mNavController;

    public static ExploreBaseFragment newInstance(int instance) {
        Bundle args = new Bundle();
        args.putInt(ARGS_INSTANCE, instance);
        ExploreBaseFragment fragment = new ExploreBaseFragment();
        fragment.setArguments(args);
        return fragment;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_explore_base, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        BottomNavigationView bottomNavigationView = (BottomNavigationView) view.findViewById(R.id.bottom_navigation);
        bottomNavigationView.setOnNavigationItemSelectedListener(this);
        final MenuItem menuItem = bottomNavigationView.getMenu().findItem(R.id.action_explore);
        menuItem.setChecked(true);

        mNavController = new FragNavController(savedInstanceState, getChildFragmentManager(), R.id.frame_container, this, 3, INDEX_POPULAR);

        onNavigationItemSelected(menuItem);

    }

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_popular:
                mNavController.switchTab(INDEX_POPULAR);
                break;
            case R.id.action_explore:
                mNavController.switchTab(INDEX_EXPLORE);
                break;
            case R.id.action_favourites:
                mNavController.switchTab(INDEX_FAVORITES);
                break;
        }
        return true;
    }

    @Override
    public Fragment getRootFragment(int i) {
        switch (i) {
            case INDEX_POPULAR:
                return PopularFragment.newInstance(0);
            case INDEX_EXPLORE:
                return ExploreFragment.newInstance(0);
            case INDEX_FAVORITES:
                return FavoritesFragment.newInstance(0);
        }
        throw new IllegalStateException("Need to send an index that we know");
    }
}