PagedListAdapter

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


RecyclerView.Adapter base class for presenting paged data from androidx.paging.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 is an easy way to provide data to the adapter, it isn't required - you can use submitList 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&lt;>(
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);
UserAdapter&lt;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&lt;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 AsyncPagedListDiffer, which provides the mapping from paging events to adapter-friendly callbacks.

Parameters
<T extends Object>

Type of the PagedLists this Adapter will receive.

<VH extends RecyclerView.ViewHolder>

A class that extends ViewHolder that will be used by the adapter.

Summary

Public fields

@Nullable PagedList<@NonNull T>

Returns the PagedList currently being displayed by the PagedListAdapter.

Public methods

void
addLoadStateListener(
    @NonNull Function2<@NonNull LoadType, @NonNull LoadStateUnit> listener
)

Add a LoadState listener to observe the loading state of the current PagedList.

int

Returns the total number of items in the data set held by the adapter.

void

This method is deprecated. Use the two argument variant instead.

void
onCurrentListChanged(
    @Nullable PagedList<@NonNull T> previousList,
    @Nullable PagedList<@NonNull T> currentList
)

Called when the current PagedList is updated.

void

Remove a previously registered LoadState listener.

void

Set the new list to be displayed.

void
submitList(
    @Nullable PagedList<@NonNull T> pagedList,
    @Nullable Runnable commitCallback
)

Set the new list to be displayed.

final @NonNull ConcatAdapter

Create a ConcatAdapter with the provided LoadStateAdapters displaying the LoadType.APPEND as a list item at the start of the presented list.

final @NonNull ConcatAdapter

Create a ConcatAdapter with the provided LoadStateAdapters displaying the LoadType.PREPEND as a list item at the end of the presented list.

final @NonNull ConcatAdapter

Create a ConcatAdapter with the provided LoadStateAdapters displaying the LoadType.PREPEND and LoadType.APPENDs as list items at the start and end respectively.

Inherited methods

From class RecyclerView.Adapter
final void
bindViewHolder(@NonNull VH holder, int position)
boolean
final @NonNull VH