AsyncPagedListDiffer

open class AsyncPagedListDiffer<T : Any>

Helper object for mapping a androidx.paging.PagedList into a RecyclerView.Adapter.

For simplicity, the PagedListAdapter wrapper class can often be used instead of the differ directly. This diff class is exposed for complex cases, and where overriding an adapter base class to support paging isn't convenient.

When consuming a LiveData of PagedList, you can observe updates and dispatch them directly to submitList. The AsyncPagedListDiffer then can present this updating data set simply for an adapter. It listens to PagedList loading callbacks, and uses DiffUtil on a background thread to compute updates as new PagedLists are received.

It provides a simple list-like API with getItem and itemCount for an adapter to acquire and present data objects.

A complete usage pattern with Room would look like this:

@Dao
interface UserDao {
    @Query("SELECT * FROM user ORDER BY lastName ASC")
    public abstract DataSource.Factory<Integer, User> usersByLastName();
}

class MyViewModel extends ViewModel {
    public final LiveData<PagedList<User>> usersList;
    public MyViewModel(UserDao userDao) {
        usersList = new LivePagedListBuilder<>(
        userDao.usersByLastName(), /* page size */20).build();
    }
}

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);
        final UserAdapter adapter = new UserAdapter();
        viewModel.usersList.observe(this, pagedList -> adapter.submitList(pagedList));
        recyclerView.setAdapter(adapter);
    }
}

class UserAdapter extends RecyclerView.Adapter&lt;UserViewHolder> {
    private final AsyncPagedListDiffer&lt;User> differ =
            new AsyncPagedListDiffer(this, DIFF_CALLBACK);
    @Override
    public int getItemCount() {
        return differ.getItemCount();
    }
    public void submitList(PagedList&lt;User> pagedList) {
        differ.submitList(pagedList);
    }
    @Override
    public void onBindViewHolder(UserViewHolder holder, int position) {
        User user = differ.getItem(position);
        if (user != null) {
            holder.bindTo(user);
        } else {
            // Null defines a placeholder item - AsyncPagedListDiffer will automatically
            // invalidate this row when the actual object is loaded from the database
            holder.clear();
        }
    }
    public static final DiffUtil.ItemCallback&lt;User> DIFF_CALLBACK =
            new DiffUtil.ItemCallback&lt;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);
        }
    }
}

Summary

Public constructors

AsyncPagedListDiffer(
    adapter: RecyclerView.Adapter<*>, 
    diffCallback: DiffUtil.ItemCallback<T>)

AsyncPagedListDiffer(
    AdapterListUpdateCallback(adapter),
    AsyncDifferConfig.Builder<T>(diffCallback).build()
)

AsyncPagedListDiffer(
    listUpdateCallback: ListUpdateCallback, 
    config: AsyncDifferConfig<T>)

Public methods

open fun addLoadStateListener(listener: (LoadType, LoadState) -> Unit): Unit

open fun addPagedListListener(listener: AsyncPagedListDiffer.PagedListListener<T>): Unit

fun addPagedListListener(callback: (PagedList<T>?, PagedList<T>?) -> Unit): Unit

open fun getItem(index: Int): T?

open fun removeLoadStateListener(listener: (LoadType, LoadState) -> Unit): Unit

open fun removePagedListListener(listener: AsyncPagedListDiffer.PagedListListener<T>): Unit