PagedListAdapter

public abstract class PagedListAdapter
extends Adapter<VH extends RecyclerView.ViewHolder>

RecyclerView.Adapter base class for presenting paged data from PagedLists in a RecyclerView.

This class is a convenience wrapper around AsyncPagedListDiffer that implements common default behavior for item counting, and listening to PagedList update callbacks.

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

PagedListAdapter listens to PagedList loading callbacks as pages are loaded, and uses DiffUtil on a background thread to compute fine grained updates as new PagedLists are received.

Handles both the internal paging of the list as more data is loaded, and updates in the form of new PagedLists.

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 = ViewModelProviders.of(this).get(MyViewModel.class);
         RecyclerView recyclerView = findViewById(R.id.user_list);
         UserAdapter<User> adapter = new UserAdapter();
         viewModel.usersList.observe(this, pagedList -> adapter.submitList(pagedList));
         recyclerView.setAdapter(adapter);
     }
 }

 class UserAdapter extends PagedListAdapter<User, UserViewHolder> {
     public UserAdapter() {
         super(DIFF_CALLBACK);
     }
     @Override
     public void onBindViewHolder(UserViewHolder holder, int position) {
         User user = getItem(position);
         if (user != null) {
             holder.bindTo(user);
         } else {
             // Null defines a placeholder item - PagedListAdapter will automatically invalidate
             // this row when the actual object is loaded from the database
             holder.clear();
         }
     }
     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);
         }
     }
 }

Summary

Protected constructors

PagedListAdapter (ItemCallback<T> diffCallback)

PagedListAdapter (AsyncDifferConfig<T> config)

Public methods

PagedList<T> getCurrentList ()

int getItemCount ()

void onCurrentListChanged (PagedList<T> currentList)

void submitList (PagedList<T> pagedList)

Protected methods

T getItem (int position)