在 Fragment 中使用 RecyclerView 而不是 Activity 会导致 E/RecyclerView: No adapter attached; 跳过布局错误

Question

I initially created and used a RecyclerView inside my CarActivity class. This worked fine, retrieved the information from the database and displayed it in the view correctly. I then modified the CarActivity class to instead use a new fragment called AllCarsFragment, and moved the RecyclerView code into the new AllCarsFragment.

The CarActivity seems to pick up the layout of the new fragment correctly, however, no data is displayed and LogCat shows the following error: E/RecyclerView: No adapter attached; skipping layout E/RecyclerView: No adapter attached; skipping layout .

I've tried moving the code between the fragments onCreateView and onViewCreated methods and messing with the code in a few other ways, however I can't figure out the fix.

I have also browsed similar questions on StackOverflow, but I'm not getting anywhere, so any help is appreciated.

CarActivity.java

public class CarActivity extends AppCompatActivity {

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

AllCarsFragment.java

public class AllCarsFragment extends Fragment {
    private static final String LOG_TAG = AllCarsFragment.class.getSimpleName();
    private CarViewModel mCarViewModel;

    @Override
    public View onCreateView(
            LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState
    ) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_all_cars, container, false);

        // Set up the recycler view to display the users saved cars
        RecyclerView recyclerView = view.findViewById(R.id.recyclerview);
        recyclerView.setLayoutManager(new LinearLayoutManager(view.getContext()));
        final CarListAdapter adapter = new CarListAdapter(view.getContext());
        recyclerView.setAdapter(adapter);

        mCarViewModel = ViewModelProviders.of(this).get(CarViewModel.class);
        mCarViewModel.getAllCars().observe(getViewLifecycleOwner(), new Observer<List<Car>>() {
            @Override
            public void onChanged(@Nullable final List<Car> cars) {
                // Update the cached copy of the cars in the adapter.
                adapter.setCars(cars);
            }
        });

        return view;
    }

    public void onViewCreated(@NonNull View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        // Configure the FAB to redirect the user to add a new car
        FloatingActionButton fab = view.findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.i(LOG_TAG, "Add Car FAB Pressed");
                NavHostFragment.findNavController(AllCarsFragment.this)
                        .navigate(R.id.add_car_dest, null);
            }
        });
    }
}

Please let me know if you need any further code or info and I'll happily update the question.

Answer 1

From your CarActivity code, it looks as though you're not actually attaching your AllCarsFragment to your CarActivity in the way that you're intending. The line setContentView(R.layout.fragment_all_cars) sets the layout file as the content view of the CarActivity, but this doesn't hook up your code in AllCarsFragment to the CarActivity. To do that, you need some extra code in CarActivity's onCreate() which does the attaching. In the docs , check out the section on "Adding a fragment to an activity".