AsyncListDiffer

class AsyncListDiffer<T>


Helper for computing the difference between two lists via DiffUtil on a background thread.

It can be connected to a RecyclerView.Adapter, and will signal the adapter of changes between sumbitted lists.

For simplicity, the ListAdapter wrapper class can often be used instead of the AsyncListDiffer directly. This AsyncListDiffer can be used for complex cases, where overriding an adapter base class to support asynchronous List diffing isn't convenient.

The AsyncListDiffer can consume the values from a LiveData of List and present the data simply for an adapter. It computes differences in list contents via DiffUtil on a background thread as new Lists are received.

Use getCurrentList to access the current List, and present its data objects. Diff results will be dispatched to the ListUpdateCallback immediately before the current list is updated. If you're dispatching list updates directly to an Adapter, this means the Adapter can safely access list items and total size via getCurrentList.

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

class UserAdapter extends RecyclerView.Adapter<UserViewHolder> {
    private final AsyncListDiffer<User> mDiffer = new AsyncListDiffer(this, DIFF_CALLBACK);
    @Override
    public int getItemCount() {
        return mDiffer.getCurrentList().size();
    }
    public void submitList(List<User> list) {
        mDiffer.submitList(list);
    }
    @Override
    public void onBindViewHolder(UserViewHolder holder, int position) {
        User user = mDiffer.getCurrentList().get(position);
        holder.bindTo(user);
    }
    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);
        }
    }
}
Parameters
<T>

Type of the lists this AsyncListDiffer will receive.

Summary

Nested types

Listener for when the current List is updated.

Public constructors

AsyncListDiffer(
    adapter: RecyclerView.Adapter,
    diffCallback: DiffUtil.ItemCallback<T!>
)

Convenience for AsyncListDiffer(new AdapterListUpdateCallback(adapter), new AsyncDifferConfig.Builder().setDiffCallback(diffCallback).build());

AsyncListDiffer(
    listUpdateCallback: ListUpdateCallback,
    config: AsyncDifferConfig<T!>
)

Create a AsyncListDiffer with the provided config, and ListUpdateCallback to dispatch updates to.

Public functions

Unit

Add a ListListener to receive updates when the current List changes.

(Mutable)List<T!>

Get the current List - any diffing to present this list has already been computed and dispatched via the ListUpdateCallback.

Unit

Remove a previously registered ListListener.

Unit
submitList(newList: (Mutable)List<T!>?)

Pass a new List to the AdapterHelper.

Unit
submitList(newList: (Mutable)List<T!>?, commitCallback: Runnable?)

Pass a new List to the AdapterHelper.

Public constructors

AsyncListDiffer

Added in 1.0.0
AsyncListDiffer(
    adapter: RecyclerView.Adapter,
    diffCallback: DiffUtil.ItemCallback<T!>
)

Convenience for AsyncListDiffer(new AdapterListUpdateCallback(adapter), new AsyncDifferConfig.Builder().setDiffCallback(diffCallback).build());

Parameters
adapter: RecyclerView.Adapter

Adapter to dispatch position updates to.

diffCallback: DiffUtil.ItemCallback<T!>

ItemCallback that compares items to dispatch appropriate animations when

AsyncListDiffer

Added in 1.0.0
AsyncListDiffer(
    listUpdateCallback: ListUpdateCallback,
    config: AsyncDifferConfig<T!>
)

Create a AsyncListDiffer with the provided config, and ListUpdateCallback to dispatch updates to.

Parameters
listUpdateCallback: ListUpdateCallback

Callback to dispatch updates to.

config: AsyncDifferConfig<T!>

Config to define background work Executor, and DiffUtil.ItemCallback for computing List diffs.

Public functions

addListListener

Added in 1.1.0
fun addListListener(listener: AsyncListDiffer.ListListener<T!>): Unit

Add a ListListener to receive updates when the current List changes.

Parameters
listener: AsyncListDiffer.ListListener<T!>

Listener to receive updates.

getCurrentList

Added in 1.0.0
fun getCurrentList(): (Mutable)List<T!>

Get the current List - any diffing to present this list has already been computed and dispatched via the ListUpdateCallback.

If a null List, or no List has been submitted, an empty list will be returned.

The returned list may not be mutated - mutations to content must be done through submitList.

Returns
(Mutable)List<T!>

current List.

removeListListener

Added in 1.1.0
fun removeListListener(listener: AsyncListDiffer.ListListener<T!>): Unit

Remove a previously registered ListListener.

Parameters
listener: AsyncListDiffer.ListListener<T!>

Previously registered listener.

submitList

Added in 1.0.0
fun submitList(newList: (Mutable)List<T!>?): Unit

Pass a new List to the AdapterHelper. Adapter updates will be computed on a background thread.

If a List is already present, a diff will be computed asynchronously on a background thread. When the diff is computed, it will be applied (dispatched to the ListUpdateCallback), and the new List will be swapped in.

Parameters
newList: (Mutable)List<T!>?

The new List.

submitList

Added in 1.1.0
fun submitList(newList: (Mutable)List<T!>?, commitCallback: Runnable?): Unit

Pass a new List to the AdapterHelper. Adapter updates will be computed on a background thread.

If a List is already present, a diff will be computed asynchronously on a background thread. When the diff is computed, it will be applied (dispatched to the ListUpdateCallback), and the new List will be swapped in.

The commit callback can be used to know when the List is committed, but note that it may not be executed. If List B is submitted immediately after List A, and is committed directly, the callback associated with List A will not be run.

Parameters
newList: (Mutable)List<T!>?

The new List.

commitCallback: Runnable?

Optional runnable that is executed when the List is committed, if it is committed.