Fragment Destroy when app go in background

Question

I face a problem, I have an activity named "MainActivity" which have 4 fragments. The problem is if I'm in fragment 2 OR 3 OR 4, and the app goes to the background like:

1. If I open bottom navigation and app go to the background, after the bottom navigation close it redirect me to the 1st fragment(Default fragment).

2. If I minimize the app and then resume it again go to 1st fragment

3. If my mobile goes to sleep and then I on it again redirect me to 1st fragment.

I cannot understand why this behaviour comes out. Please suggest me the possible solutions.

Here is the main activity code :

public class ContainerActivity extends AppCompatActivity
    implements BottomNavigationView.OnNavigationItemSelectedListener{

private Fragment fragment;
private BottomNavigationView bottomNavigationView;
private RestaurantListFragment restaurantListFragment;
private String completeAddress, cityName, countryName, latitude, longitude, nickName, addressLabel, locationType, currentLock;

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

    if(getIntent().getExtras() != null){
        latitude = getIntent().getExtras().getString("latitude");
        longitude = getIntent().getExtras().getString("longitude");
        completeAddress = getIntent().getExtras().getString("complete_address");
        cityName = getIntent().getExtras().getString("city_name");
        countryName = getIntent().getExtras().getString("country_name");
        nickName = getIntent().getExtras().getString("nick_name");
        addressLabel = getIntent().getExtras().getString("label");
        locationType = getIntent().getExtras().getString("location_type");
        currentLock = getIntent().getExtras().getString("current_lock");

        Bundle bundle = new Bundle();
        bundle.putString("latitude", latitude);
        bundle.putString("longitude", longitude);
        bundle.putString("complete_address", completeAddress);
        bundle.putString("city_name", cityName);
        bundle.putString("country_name", countryName);
        bundle.putString("nick_name", nickName);
        bundle.putString("label", addressLabel);
        bundle.putString("location_type", locationType);
        bundle.putString("current_lock", currentLock);

        restaurantListFragment.setArguments(bundle);
    }
}

@Override
protected void onResume() {
    super.onResume();
    getSupportFragmentManager().beginTransaction()
            .replace(R.id.fragment_container, restaurantListFragment).addToBackStack(null).commit();
}

private void initView() {
    bottomNavigationView = findViewById(R.id.btoom_navigation_view);
    bottomNavigationView.setOnNavigationItemSelectedListener(this);
    bottomNavigationView.setSelectedItemId(R.id.home);
    restaurantListFragment = new RestaurantListFragment();
}

public void openRestaurantMenuFragment(Bundle bundle) {
    RestaurantMenuFragment restaurantMenuFragment = new RestaurantMenuFragment();
    restaurantMenuFragment.setArguments(bundle);

    getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.fragment_container, restaurantMenuFragment)
            .addToBackStack(null)
            .commit();
}

public void openFoodListOrDetailFrgment() {
    getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.fragment_container, new FoodDetailFragment())
            .addToBackStack(null)
            .commit();
}

public void openCart(){
    getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.fragment_container, new MyOrderFragment())
            .addToBackStack(null)
            .commit();
}

public void openCompleteItemDetailFragment(){
         bottomNavigationView.setVisibility(View.GONE);
}

public void showBottomNavigation(){
    if(bottomNavigationView.getVisibility() == View.GONE){
        bottomNavigationView.setVisibility(View.VISIBLE);
    }
}

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    fragment = getSupportFragmentManager().findFragmentById(R.id.fragment_container);
    switch (item.getItemId()) {
        case R.id.home:
            if ((getSupportFragmentManager().findFragmentById(R.id.fragment_container)) != null && !(fragment instanceof RestaurantListFragment)){
                getSupportFragmentManager().beginTransaction()
                        .replace(R.id.fragment_container, new RestaurantListFragment()).addToBackStack(null).commit();
            }
            break;
        case R.id.explore:


            break;
        case R.id.profile:

            getSupportFragmentManager()
                    .beginTransaction()
                    .replace(R.id.fragment_container, new ProfileFragment())
                    .addToBackStack(null)
                    .commit();
            break;

    }
    return true;
}

@Override
public void onBackPressed() {
    Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.fragment_container);

    if(fragment instanceof RestaurantListFragment){
        getSupportFragmentManager().popBackStack(0, getSupportFragmentManager().POP_BACK_STACK_INCLUSIVE);
    }
    if(fragment instanceof CompleteFoodItemDetailFragment || fragment instanceof GoogleMapFragment){
        if(bottomNavigationView.getVisibility() == View.GONE){
            bottomNavigationView.setVisibility(View.VISIBLE);
        }
    }

    super.onBackPressed();
}

}

Answer 1

In your Question, you are saying when activity is resumed from the background the default fragment opens (restaurantListFragment) I am supposing. it's due to

onResume() Method

@Override
protected void onResume() {
    super.onResume();
    getSupportFragmentManager().beginTransaction()
            .replace(R.id.fragment_container, restaurantListFragment).addToBackStack(null).commit();
}

replace it with(fragment will only be changed if it's empty or detached at some point)

private fm;
initViews(){
   fm = supportFragmentManager.beginTransaction();
}

    @Override
    protected void onResume() {
        super.onResume();

        if(fm.isEmpty() || restaurantListFragment.isDetached()){
            fm.replace(R.id.fragment_container, restaurantListFragment).addToBackStack(null).commit();
        }
    }

also replace the fragment in onCreate

@Override
    protected void onCreate(Bundle savedInstanceState){
    ...
    //below initViews();
    ...
    fm.replace(R.id.fragment_container, restaurantListFragment).addToBackStack(null).commit();
    }