HomeFragment cannot be converted to Fragment

I have problem with connecting FirestoreUI with BottomNavigationBar. I don't know how to implement OnCreateView to modified HomeFragment which look like this-

public class HomeFragment extends AppCompatActivity {
    private FirebaseFirestore db = FirebaseFirestore.getInstance();
    private CollectionReference textRef = db.collection("text");

    private NoteAdapter adapter;

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

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

        setUpRecyclerView();
    }

    private void setUpRecyclerView() {
        Query query = textRef.orderBy("title", Query.Direction.DESCENDING);

        FirestoreRecyclerOptions<Note> options = new FirestoreRecyclerOptions.Builder<Note>()
                .setQuery(query, Note.class)
                .build();

        adapter = new NoteAdapter(options);
        RecyclerView  recyclerView = findViewById(R.id.recycler_view);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(adapter);
    }

    @Override
    protected void onStart() {
        super.onStart();
        adapter.startListening();
    }

    @Override
    protected void onStop() {
        super.onStop();
        adapter.stopListening();
    }
}

To compare another working fragment (GameFragment)-

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

And BottomNavigation method-

private BottomNavigationView.OnNavigationItemSelectedListener navListener =
    new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            Fragment selectedFragment = null;

            switch (item.getItemId()) {
                case R.id.nav_home:
                    selectedFragment = new HomeFragment();
                    break;
                case R.id.nav_ranking:
                    selectedFragment = new RankingFragment();
                    break;
                case R.id.nav_user:
                    selectedFragment = new UserFragment();
                    break;
            }

            getSupportFragmentManager()
                    .beginTransaction()
                    .replace(R.id.fragment_container,
                    selectedFragment)
                    .commit();

            return true;
        }
    };

I tried to paste

> import androidx.fragment.app.Fragment;

into public class HomeFragment extends AppCompatActivity, Fragment {} but then all code crash.
Please help, thanks.

The problem is that you are trying to replace a fragment with an activity.

I'm going to extract some code and point out what the problem is:

//.....
switch (item.getItemId()) {
case R.id.nav_home:
selectedFragment = new HomeFragment(); // <-- HomeFragment is of type: AppCompatActivity
break;
case R.id.nav_ranking:
selectedFragment = new RankingFragment(); // <-- RankingFragment is of type: Fragment
break;
case R.id.nav_user:
selectedFragment = new UserFragment(); // <-- UserFragment is of type: Fragment
break;
}
getSupportFragmentManager() // <-- You're asking the SupportFragmentManager to replace your current fragment with another
.beginTransaction()
.replace(R.id.fragment_container,
selectedFragment) // <-- You can replace a fragment with another fragment, but not with an Activity
.commit();
//...

So what I suggest is that you rename HomeFragment to HomeActivity and make a new fragment that extends from Fragment and use it like you do with the other fragments you have.

To outline what I mean:

• HomeActivity extends AppCompatActivity -> with a view R.id.fragment_container, also add the code here for fragment replacement like you already have.
• HomeFragment extends Fragment
• RankingFragment extends Fragment
• UserFragment extends Fragment