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ListAdapter

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

java.lang.Object
   ↳ androidx.recyclerview.widget.RecyclerView.Adapter<VH extends androidx.recyclerview.widget.RecyclerView.ViewHolder>
     ↳ androidx.recyclerview.widget.ListAdapter<T, VH extends androidx.recyclerview.widget.RecyclerView.ViewHolder>


RecyclerView.Adapter base class for presenting List data in a RecyclerView, including computing diffs between Lists on a background thread.

This class is a convenience wrapper around AsyncListDiffer that implements Adapter common default behavior for item access and counting.

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

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

 class UserAdapter extends ListAdapter<User, UserViewHolder> {
     public UserAdapter() {
         super(User.DIFF_CALLBACK);
     }
     @Override
     public void onBindViewHolder(UserViewHolder holder, int position) {
         holder.bindTo(getItem(position));
     }
     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);
         }
     }
 }
Advanced users that wish for more control over adapter behavior, or to provide a specific base class should refer to AsyncListDiffer, which provides custom mapping from diff events to adapter positions.

Summary

Protected constructors

ListAdapter(ItemCallback<T> diffCallback)
ListAdapter(AsyncDifferConfig<T> config)

Public methods

List<T> getCurrentList()

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

int getItemCount()

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

void onCurrentListChanged(List<T> previousList, List<T> currentList)

Called when the current List is updated.

void submitList(List<T> list)

Submits a new list to be diffed, and displayed.

void submitList(List<T> list, Runnable commitCallback)

Set the new list to be displayed.

Protected methods

T getItem(int position)

Inherited methods

Protected constructors

ListAdapter

protected ListAdapter (ItemCallback<T> diffCallback)

Parameters
diffCallback ItemCallback

ListAdapter

protected ListAdapter (AsyncDifferConfig<T> config)

Parameters
config AsyncDifferConfig

Public methods

getCurrentList

public 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> The list currently being displayed.

getItemCount

public int getItemCount ()

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

Returns
int The total number of items in this adapter.

onCurrentListChanged

public void onCurrentListChanged (List<T> previousList, 
                List<T> currentList)

Called when the current List is updated.

If a null List is passed to submitList(List), or no List has been submitted, the current List is represented as an empty List.

Parameters
previousList List: List that was displayed previously.

currentList List: new List being displayed, will be empty if null was passed to submitList(List).

See also:

submitList

public void submitList (List<T> list)

Submits a new list to be diffed, and displayed.

If a list is already being displayed, a diff will be computed on a background thread, which will dispatch Adapter.notifyItem events on the main thread.

Parameters
list List: The new list to be displayed.

submitList

public void submitList (List<T> list, 
                Runnable commitCallback)

Set the new list to be displayed.

If a List is already being displayed, a diff will be computed on a background thread, which will dispatch Adapter.notifyItem events on the main thread.

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
list List: The new list to be displayed.

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

Protected methods

getItem

protected T getItem (int position)

Parameters
position int

Returns
T