AsyncListDiffer
open class AsyncListDiffer<T : Any!>
kotlin.Any | |
↳ | androidx.recyclerview.widget.AsyncListDiffer |
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 List
s 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); } } }
Summary
Nested classes | |
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abstract |
Listener for when the current List is updated. |
Public constructors | |
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<init>(@NonNull adapter: RecyclerView.Adapter<RecyclerView.ViewHolder!>, @NonNull diffCallback: DiffUtil.ItemCallback<T>) Convenience for |
|
<init>(@NonNull listUpdateCallback: ListUpdateCallback, @NonNull config: AsyncDifferConfig<T>) Create a AsyncListDiffer with the provided config, and ListUpdateCallback to dispatch updates to. |
Public methods | |
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open Unit |
addListListener(@NonNull listener: AsyncListDiffer.ListListener<T>) Add a ListListener to receive updates when the current List changes. |
open MutableList<T> |
Get the current List - any diffing to present this list has already been computed and dispatched via the ListUpdateCallback. |
open Unit |
removeListListener(@NonNull listener: AsyncListDiffer.ListListener<T>) Remove a previously registered ListListener. |
open Unit |
submitList(@Nullable newList: MutableList<T>?) Pass a new List to the AdapterHelper. |
open Unit |
submitList(@Nullable newList: MutableList<T>?, @Nullable commitCallback: Runnable?) Pass a new List to the AdapterHelper. |
Public constructors
<init>
AsyncListDiffer(
@NonNull adapter: RecyclerView.Adapter<RecyclerView.ViewHolder!>,
@NonNull diffCallback: DiffUtil.ItemCallback<T>)
Convenience for AsyncListDiffer(new AdapterListUpdateCallback(adapter), new AsyncDifferConfig.Builder().setDiffCallback(diffCallback).build());
Parameters | |
---|---|
adapter |
RecyclerView.Adapter<RecyclerView.ViewHolder!>: Adapter to dispatch position updates to. |
diffCallback |
DiffUtil.ItemCallback<T>: ItemCallback that compares items to dispatch appropriate animations when |
<init>
AsyncListDiffer(
@NonNull listUpdateCallback: ListUpdateCallback,
@NonNull 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 methods
addListListener
open fun addListListener(@NonNull listener: AsyncListDiffer.ListListener<T>): Unit
Add a ListListener to receive updates when the current List changes.
Parameters | |
---|---|
listener |
AsyncLis |