belongs to Maven artifact com.android.support:recyclerview-v7:28.0.0-alpha1
AsyncListDiffer
public
class
AsyncListDiffer
extends Object
java.lang.Object | |
↳ | android.support.v7.recyclerview.extensions.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 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 = ViewModelProviders.of(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); } } }
See also:
Summary
Public constructors | |
---|---|
AsyncListDiffer(Adapter adapter, ItemCallback<T> diffCallback)
Convenience for
|
|
AsyncListDiffer(ListUpdateCallback listUpdateCallback, AsyncDifferConfig<T> config)
Create a AsyncListDiffer with the provided config, and ListUpdateCallback to dispatch updates to. |
Public methods | |
---|---|
List<T>
|
getCurrentList()
Get the current List - any diffing to present this list has already been computed and dispatched via the ListUpdateCallback. |
void
|
submitList(List<T> newList)
Pass a new List to the AdapterHelper. |
Inherited methods | |
---|---|
From
class
java.lang.Object
|
Public constructors
AsyncListDiffer
AsyncListDiffer (Adapter adapter, ItemCallback<T> diffCallback)
Convenience for
AsyncListDiffer(new AdapterListUpdateCallback(adapter),
new AsyncDifferConfig.Builder().setDiffCallback(diffCallback).build());
Parameters | |
---|---|
adapter |
Adapter : Adapter to dispatch position updates to. |
diffCallback |
ItemCallback : ItemCallback that compares items to dispatch appropriate animations when |
See also:
AsyncListDiffer
AsyncListDiffer (ListUpdateCallback listUpdateCallback, AsyncDifferConfig<T> config)
Create a AsyncListDiffer with the provided config, and ListUpdateCallback to dispatch updates to.
Parameters | |
---|---|
listUpdateCallback |
ListUpdateCallback : Callback to dispatch updates to. |
config |
AsyncDifferConfig : Config to define background work Executor, and DiffUtil.ItemCallback for
computing List diffs. |
See also:
Public methods
getCurrentList
List<T> getCurrentList ()
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(List)
.
Returns | |
---|---|
List<T> |
current List. |
submitList
void submitList (List<T> newList)
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 |
List : The new List.
|