Android BottomNavigation fragment show/hide after App (screen) rotate

Shifatul :

I am trying to simulate App (screen) rotate, but after the screen is rotated, the BottomNavigation fragments won't work anymore.

I have the following Array / vars

private Fragment[] fragments = new Fragment[]{new HomeFragment(), new MapFragment(), new SavedFragment(), new NotificationsFragment()};
private int selected = -1;

In onCreateView I am calling...

// open first Fragment when app starts
if (savedInstanceState == null) switchFragment(0, ShoutsHomeFragment.TAG); 
else selected = savedInstanceState.getInt(SELECTED_FRAGMENT);

switchFragment looks like

private void switchFragment(int index, String tag) {
    FragmentTransaction transaction = fragmentManager.beginTransaction();
    Fragment fragment = fragmentManager.findFragmentByTag(tag);
    // creating for the first time
    if (fragment == null) transaction.add(R.id.tab_fragment_container, fragments[index], tag);
    if (selected >= 0) transaction.hide(fragments[selected]);   // <--- don't work
    if (fragment != null) transaction.show(fragment);           // <--- don't work
    transaction.commit();
    selected = index;
}

So, transaction.hide and transaction.show is not working after rotating the screen, it stays on the same Fragment when I tap on other items on the BottomNavigation

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    switch (item.getItemId()) {
        case R.id.navigation_shouts_home:
            switchFragment(0, HomeFragment.TAG);
            return true;
        case R.id.navigation_heat_map:
            switchFragment(1, MapFragment.TAG);
            return true;
        case R.id.navigation_loved:
            switchFragment(2, SavedFragment.TAG);
            return true;
        case R.id.navigation_notifications:
            switchFragment(3, NotificationsFragment.TAG);
            return true;
}

@Override
public void onSaveInstanceState(@NonNull Bundle outState) {
    outState.putInt(SELECTED_FRAGMENT, selected);
    super.onSaveInstanceState(outState);
}

I programmed it this way so that I can retain Fragments (scroll) position when switching between items on BottomNavigation. So I want to show/hide instead of creating new Instance every time. Any help is appreciated.

user2836202 :

When you rotate the screen, all of your activities and all of your non-retained fragments are put through the whole lifecycle. This means your private Fragment[] fragments... is also recreated. Your Fragments in your list are no longer the fragments in the FragmentManager. This means hide is not going to work the way you have it being called and the top-most Fragment will always be the one that is visible. If you use the TAG method, it will probably work.

String getFragmentTagByIndex(final int index) {
    switch (index) {
       // Make return tag.
    }
}

{
// inside switchFragment
    final Fragment visibleFragment = transaction.findFragmentByTag(getFragmentTagByIndex(selected));
    transaction.hide(visibleFragment);
}

You are essentially trying to implement a ViewPager with a FragmentPagerAdapter I would recommend you use the FragmentPagerAdapter