ListAdapter

abstract class ListAdapter<T, VH : RecyclerView.ViewHolder?> : RecyclerView.Adapter

kotlin.Any
   ↳ androidx.recyclerview.widget.RecyclerView.Adapter
     ↳ androidx.recyclerview.widget.ListAdapter

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 is an easy way to provide data to the adapter, it isn't required - you can use submitList 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.
Parameters
<T>

Type of the Lists this Adapter will receive.
<VH : RecyclerView.ViewHolder?>

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

Summary

Protected constructors

Public functions
(Mutable)List<T!>

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

Returns the total number of items in the data set held by the adapter.
Unit
onCurrentListChanged(
    previousList: (Mutable)List<T!>,
    currentList: (Mutable)List<T!>
)

Called when the current List is updated.
Unit
submitList(list: (Mutable)List<T!>?)

Submits a new list to be diffed, and displayed.
Unit
submitList(list: (Mutable)List<T!>?, commitCallback: Runnable?)

Set the new list to be displayed.

Protected functions
T!
getItem(position: Int)

Inherited functions
From androidx.recyclerview.widget.RecyclerView.Adapter
Unit
bindViewHolder(holder: VH, position: Int)

This method internally calls onBindViewHolder to update the ViewHolder contents with the item at the given position and also sets up some private fields to be used by RecyclerView.
VH
createViewHolder(parent: ViewGroup, viewType: Int)

This method calls onCreateViewHolder to create a new ViewHolder and initializes some private fields to be used by RecyclerView.
Int
findRelativeAdapterPositionIn(
    adapter: RecyclerView.Adapter<RecyclerView.ViewHolder!>,
    viewHolder: RecyclerView.ViewHolder,
    localPosition: Int
)

Returns the position of the given ViewHolder in the given Adapter.
Long
getItemId(position: Int)

Return the stable ID for the item at position.
Int
getItemViewType(position: Int)

Return the view type of the item at position for the purposes of view recycling.
RecyclerView.Adapter.StateRestorationPolicy

Returns when this Adapter wants to restore the state.
Boolean

Returns true if one or more observers are attached to this adapter.
Boolean

Returns true if this adapter publishes a unique long value that can act as a key for the item at a given position in the data set.
Unit

Notify any registered observers that the data set has changed.
Unit

Notify any registered observers that the item at position has changed.
Unit
notifyItemChanged(position: Int, payload: Any?)

Notify any registered observers that the item at position has changed with an optional payload object.
Unit

Notify any registered observers that the item reflected at position has been newly inserted.
Unit
notifyItemMoved(fromPosition: Int, toPosition: Int)

Notify any registered observers that the item reflected at fromPosition has been moved to toPosition.
Unit
notifyItemRangeChanged(positionStart: Int, itemCount: Int)

Notify any registered observers that the itemCount items starting at position positionStart have changed.
Unit
notifyItemRangeChanged(positionStart: Int, itemCount: Int, payload: Any?)

Notify any registered observers that the itemCount items starting at position positionStart have changed.
Unit
notifyItemRangeInserted(positionStart: Int, itemCount: Int)

Notify any registered observers that the currently reflected itemCount items starting at positionStart have been newly inserted.
Unit
notifyItemRangeRemoved(positionStart: Int, itemCount: Int)

Notify any registered observers that the itemCount items previously located at positionStart have been removed from the data set.
Unit

Notify any registered observers that the item previously located at position has been removed from the data set.
Unit

Called by RecyclerView when it starts observing this Adapter.
abstract Unit
onBindViewHolder(holder: VH, position: Int)

Called by RecyclerView to display the data at the specified position.
Unit
onBindViewHolder(holder: VH, position: Int, payloads: (Mutable)List<Any!>)

Called by RecyclerView to display the data at the specified position.
abstract VH
onCreateViewHolder(parent: ViewGroup, viewType: Int)

Called when RecyclerView needs a new ViewHolder of the given type to represent an item.
Unit

Called by RecyclerView when it stops observing this Adapter.
Boolean

Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled due to its transient state.
Unit

Called when a view created by this adapter has been attached to a window.
Unit

Called when a view created by this adapter has been detached from its window.
Unit
onViewRecycled(holder: VH)

Called when a view created by this adapter has been recycled.
Unit

Register a new observer to listen for data changes.
Unit
setHasStableIds(hasStableIds: Boolean)

Indicates whether each item in the data set can be represented with a unique identifier of type java.lang.Long.
Unit

Sets the state restoration strategy for the Adapter.
Unit

Unregister an observer currently listening for data changes.

Protected constructors

ListAdapter

Added in 1.0.0
protected ListAdapter(config: AsyncDifferConfig<T!>)

ListAdapter

Added in 1.0.0
protected ListAdapter(diffCallback: DiffUtil.ItemCallback<T!>)

Public functions

getCurrentList

Added in 1.1.0
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!>

The list currently being displayed.
See also
onCurrentListChanged

getItemCount

Added in 1.4.0
fun getItemCount(): Int

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

Added in 1.1.0
fun onCurrentListChanged(
    previousList: (Mutable)List<T!>,
    currentList: (Mutable)List<T!>
): Unit

Called when the current List is updated.

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

Parameters
previousList: (Mutable)List<T!>

List that was displayed previously.
currentList: (Mutable)List<T!>

new List being displayed, will be empty if null was passed to submitList.
See also
getCurrentList

submitList

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

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: (Mutable)List<T!>?

The new list to be displayed.

submitList

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

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: (Mutable)List<T!>?

The new list to be displayed.
commitCallback: Runnable?

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

Protected functions

getItem

Added in 1.0.0
protected fun getItem(position: Int): T!