java - HomeFragment 无法转换为 Fragment

Question

我在将 FirestoreUI 与 BottomNavigationBar 连接时遇到问题。我不知道如何实现OnCreateView来修改HomeFragment，如下所示-

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();
    }
}

比较另一个工作 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);
    }
}

和BottomNavigation方法-

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;
        }
    };

我尝试粘贴

import androidx.fragment.app.Fragment;

进入 public class HomeFragment extends AppCompatActivity, Fragment {} 但随后所有代码崩溃。请帮忙，谢谢。

Answer 1

问题是您正在尝试用 Activity 替换 fragment 。

我将提取一些代码并指出问题所在:

//.....
             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();
//...

所以我建议您将 HomeFragment 重命名为 HomeActivity 并创建一个从 Fragment 扩展的新 fragment ，并像使用其他 fragment 一样使用它。

概述我的意思:

• HomeActivity 扩展了 AppCompatActivity -> 使用 View R.id.fragment_container，还可以像您已有的那样在此处添加用于 fragment 替换的代码。
• HomeFragment 扩展 Fragment
• RankingFragment 扩展 Fragment
• UserFragment 扩展 Fragment