BottomNavigationView - How to avoid recreation of Fragments and reuse them

I had similar issue, but this code solved my problem.

public class MainActivity extends AppCompatActivity {

    boolean doubleBackToExitPressedOnce = false;
    final Fragment fragment1 = new HomeFragment();
    final Fragment fragment2 = new DashboardFragment();
    final Fragment fragment3 = new NotificationsFragment();
    final FragmentManager fm = getSupportFragmentManager();
    Fragment active = fragment1;
    BottomNavigationView navigation;

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

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
        setFragment(fragment1, "1", 0);
    }


    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    setFragment(fragment1, "1", 0);
                    return true;
                case R.id.navigation_dashboard:
                    setFragment(fragment2, "2", 1);
                    return true;
                case R.id.navigation_notifications:
                    setFragment(fragment3, "3", 2);
                    return true;
            }
            return false;
        }
    };

    public void setFragment(Fragment fragment, String tag, int position) {
        if (fragment.isAdded()) {
            fm.beginTransaction().hide(active).show(fragment).commit();
        } else {
            fm.beginTransaction().add(R.id.main_container, fragment, tag).commit();
        }
        navigation.getMenu().getItem(position).setChecked(true);
        active = fragment;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.action_settings) {
            startActivity(new Intent(MainActivity.this, SettingsActivity.class));
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onBackPressed() {
        if (active == fragment1) {
            if (doubleBackToExitPressedOnce) {
                super.onBackPressed();
                return;
            }
            this.doubleBackToExitPressedOnce = true;
            Toast.makeText(this, "Please click BACK again to exit", Toast.LENGTH_SHORT).show();
        } else {
            setFragment(fragment1, "1", 0);
        }
    }
}

I wouldn't keep the fragment instances globally. Instead add a tag to the fragment when creating them

getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.container, new PlaceholderFragment(), TAG_PLACEHOLDER)
            .commit();

Then you can always retrieve it like this:

Fragment fragment = getSupportFragmentManager().findFragmentByTag(TAG_PLACEHOLDER);
    if (fragment == null) {
        fragment = new PlaceholderFragment();
    }
    getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.container, fragment, TAG_PLACEHOLDER)
            .commit();

UPDATE: I updated my answer and to provide a complete solution:

private static final String TAG_FRAGMENT_ONE = "fragment_one";
private static final String TAG_FRAGMENT_TWO = "fragment_two";
private static final String TAG_FRAGMENT_THREE = "fragment_three";

private FragmentManager fragmentManager;
private Fragment currentFragment;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // instantiate the fragment manager
    fragmentManager = getSupportFragmentManager();

    Fragment fragment = fragmentManager.findFragmentByTag(TAG_FRAGMENT_ONE);
    if (fragment == null) {
        fragment = FirstFragment.newInstance();
    }
    replaceFragment(fragment, TAG_FRAGMENT_ONE);

    bottomNavigationView = (BottomNavigationView) findViewById(R.id.navigation);
    bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            Fragment fragment = null;
            switch (item.getItemId()) {
                case R.id.menu_dialer:
                    // I'm aware that this code can be optimized by a method which accepts a class definition and returns the proper fragment
                    Fragment fragment = fragmentManager.findFragmentByTag(TAG_FRAGMENT_ONE);
                    if (fragment == null) {
                        fragment = FirstFragment.newInstance();
                    }
                    replaceFragment(fragment, TAG_FRAGMENT_ONE);
                    break;
                case R.id.menu_email:
                    Fragment fragment = fragmentManager.findFragmentByTag(TAG_FRAGMENT_TWO);
                    if (fragment == null) {
                        fragment = SecondFragment.newInstance();
                    }
                    replaceFragment(fragment, TAG_FRAGMENT_TWO);
                    break;
                case R.id.menu_map:
                    Fragment fragment = fragmentManager.findFragmentByTag(TAG_FRAGMENT_THREE);
                    if (fragment == null) {
                        fragment = ThirdFragment.newInstance();
                    }
                    replaceFragment(fragment, TAG_FRAGMENT_THREE);
                    break;
            }
            return true;
        }
    });
}

private void replaceFragment(@NonNull Fragment fragment, @NonNull String tag) {
    if (!fragment.equals(currentFragment)) {
        fragmentManager
            .beginTransaction()
            .replace(R.id.frameLayout, fragment, tag)
            .commit();
        currentFragment = fragment;
    }
}

ADDITIONAL INFO: If you want to be sure that the fragment states don't change and if you also want to be able to swipe the fragments you should consider using a ViewPager with a FragmentStatePagerAdapter and change the current fragment in the adapter with every click event

I wrote a Kotlin Extension function for FragmentManager class

fun FragmentManager.switch(containerId: Int, newFrag: Fragment, tag: String) {

    var current = findFragmentByTag(tag)
    beginTransaction()
        .apply {

            //Hide the current fragment
            primaryNavigationFragment?.let { hide(it) }

            //Check if current fragment exists in fragmentManager
            if (current == null) {
                current = newFrag
                add(containerId, current!!, tag)
            } else {
                show(current!!)
            }
        }
        .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
        .setPrimaryNavigationFragment(current)
        .setReorderingAllowed(true)
        .commitNowAllowingStateLoss()
}

This can be called by supportFragmentManager.swtich(R.id.container,newFrag,newFrag.TAG) from onNavigationItemSelected

All the previous answers are using fragmentTransaction.replace(...). This will replace the current fragment by destroying it (which is causing the problem). Therefore all those solutions won't actually work.

This is the closest thing I could get to as a solution for this problem:

private void selectContentFragment(Fragment fragmentToSelect)
{
    FragmentTransaction fragmentTransaction = this.getSupportFragmentManager().beginTransaction();

    if (this.getSupportFragmentManager().getFragments().contains(fragmentToSelect)) {
        // Iterate through all cached fragments.
        for (Fragment cachedFragment : this.getSupportFragmentManager().getFragments()) {
            if (cachedFragment != fragmentToSelect) {
                // Hide the fragments that are not the one being selected.
                fragmentTransaction.hide(cachedFragment);
            }
        }
        // Show the fragment that we want to be selected.
        fragmentTransaction.show(fragmentToSelect);
    } else {
        // The fragment to be selected does not (yet) exist in the fragment manager, add it.
        fragmentTransaction.add(R.id.fragment_container, fragmentToSelect);
    }

    fragmentTransaction.commit();
}

To make this work, you should keep track of the fragments in an array (or in separate variables) in your Activity. I for reference pre-instantiated all fragments in a SparseArray.