recyclerview/androidx.recyclerview.widget/ListAdapter

ListAdapter

abstract class ListAdapter<T, VH : RecyclerView.ViewHolder?> : RecyclerView.Adapter<VH> (source)

RecyclerView.Adapter base class for presenting List data in a RecyclerView, including computing diffs between Lists on a background thread.

This class is a convenience wrapper around AsyncListDiffer that implements Adapter common default behavior for item access and counting.

While using a LiveData is an easy way to provide data to the adapter, it isn't required - you can use submitList when new lists are available.

A complete usage pattern with Room would look like this:

@Dao
interface UserDao {
    @Query("SELECT * FROM user ORDER BY lastName ASC")
    public abstract LiveData<List<User>> usersByLastName();
}

class MyViewModel extends ViewModel {
    public final LiveData<List<User>> usersList;
    public MyViewModel(UserDao userDao) {
        usersList = userDao.usersByLastName();
    }
}

class MyActivity extends AppCompatActivity {
    @Override
    public void onCreate(Bundle savedState) {
        super.onCreate(savedState);
        MyViewModel viewModel = new ViewModelProvider(this).get(MyViewModel.class);
        RecyclerView recyclerView = findViewById(R.id.user_list);
        UserAdapter<User> adapter = new UserAdapter();
        viewModel.usersList.observe(this, list -> adapter.submitList(list));
        recyclerView.setAdapter(adapter);
    }
}

class UserAdapter extends ListAdapter<User, UserViewHolder> {
    public UserAdapter() {
        super(User.DIFF_CALLBACK);
    }
    @Override
    public void onBindViewHolder(UserViewHolder holder, int position) {
        holder.bindTo(getItem(position));
    }
    public static final DiffUtil.ItemCallback<User> DIFF_CALLBACK =
            new DiffUtil.ItemCallback<User>() {
        @Override
        public boolean areItemsTheSame(
                @NonNull User oldUser, @NonNull User newUser) {
            // User properties may have changed if reloaded from the DB, but ID is fixed
            return oldUser.getId() == newUser.getId();
        }
        @Override
        public boolean areContentsTheSame(
                @NonNull User oldUser, @NonNull User newUser) {
            // NOTE: if you use equals, your object must properly override Object#equals()
            // Incorrectly returning false here will result in too many animations.
            return oldUser.equals(newUser);
        }
    }
}

Advanced users that wish for more control over adapter behavior, or to provide a specific base class should refer to AsyncListDiffer, which provides custom mapping from diff events to adapter positions.