我想在我的Fragment的onViewCreated方法中访问ViewModel类（它扩展了AndroidViewModel）。下面一行代码应该像android文档说的那样工作。但它没有！

ProductListViewModel viewModel = new ViewModelProvider(this).get(ProductListViewModel.class);

显然最近ViewModelProvider构造函数发生了变化。它需要一个ViewModelProvider.Factory实现作为第二个参数。为什么需要ViewModelProvider.Factory实现以及如何实现？
下面是我的Fragment类：

public class HomeFragment extends Fragment {

    private HomeListAdapter homeListAdapter;

    public HomeFragment() {
        // Required empty public constructor
    }

    public static HomeFragment newInstance() {
        return new HomeFragment();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_home, container, false);

        homeListAdapter = new HomeListAdapter(getContext());

        RecyclerView homeRecyclerView = view.findViewById(R.id.rv_products);
        homeRecyclerView.setAdapter(homeListAdapter);
        homeRecyclerView.setLayoutManager(new LinearLayoutManager(getContext()));

        return view;
    }

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

        ProductListViewModel viewModel = new ViewModelProvider(this).get(ProductListViewModel.class);

        viewModel.getAllProducts().observe(this, new Observer<List<Product>>() {
            @Override
            public void onChanged(List<Product> products) {
                homeListAdapter.setProducts(products);
            }
        });
    }
}

这是我的ViewModel：

public class ProductListViewModel extends AndroidViewModel {

    private ProductRepository mRepository;
    private LiveData<List<Product>> mAllProducts;

    public ProductListViewModel(@NonNull Application application) {
        super(application);

        mRepository = new ProductRepository(application);
        mAllProducts = mRepository.getAllProducts();
    }

    public LiveData<List<Product>> getAllProducts() {
        return mAllProducts;
    }

    public void insert(Product product) {
        mRepository.insert(product);
    }
}