Как go в другой фрагмент из MapsActivity

Question

У меня есть mapsActivity, которая является MainActivity, которая расширяет фрагмент, и я хочу go на другой фрагмент:

ЗДЕСЬ МОЙ XML:

<fragment
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:map="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >

<com.google.android.material.appbar.AppBarLayout
    android:id="@+id/bar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="?android:attr/windowBackground">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/top_navigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorAccent"
        map:labelVisibilityMode="unlabeled"
        map:menu="@menu/top_nav"/>

</com.google.android.material.appbar.AppBarLayout>

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/fragment_container" />

Вот мой Java код:

public class MainActivity extends AppCompatActivity //FragmentActivity
implements
    OnMapReadyCallback,
    GoogleApiClient.ConnectionCallbacks {

private GoogleMap mMap;
AppBarLayout appBarLayout;

BottomNavigationView bottomNavigation;
Fragment selectedfragment = null;
ImageView settings;

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

bottomNavigation = findViewById (R.id.top_navigation); bottomNavigation.setOnNavigationItemSelectedListener (navigationItemSelectedListener);

    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);

private BottomNavigationView.OnNavigationItemSelectedListener        navigationItemSelectedListener=
    new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {

            switch (menuItem.getItemId()) {
                case R.id.ic_home:
                    selectedfragment = new HomeFragment();
                    editor.apply();
                    break;

                case R.id.ic_chats:
                    selectedfragment = new ChatsFragment();
                    break;
                case R.id.settings:

                    selectedfragment = null;
                    startActivity(new Intent(MainActivity.this, OptionsActivity.class));
                    break;
            }
            if (selectedfragment != null){
                      getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        selectedfragment).commit();
            }
            return true;
        }
    };

Намерение работает нормально, только транзакция с двумя фрагментами не будет работать