ConcatAdapter

Kotlin |Java

class ConcatAdapter : RecyclerView.Adapter<RecyclerView.ViewHolder!>

kotlin.Any
↳	androidx.recyclerview.widget.RecyclerView.Adapter<androidx.recyclerview.widget.RecyclerView.ViewHolder>
	↳	androidx.recyclerview.widget.ConcatAdapter

An Adapter implementation that presents the contents of multiple adapters in sequence.

MyAdapter adapter1 = ...;
  AnotherAdapter adapter2 = ...;
  ConcatAdapter concatenated = new ConcatAdapter(adapter1, adapter2);
  recyclerView.setAdapter(concatenated);
  

By default, ConcatAdapter isolates view types of nested adapters from each other such that it will change the view type before reporting it back to the RecyclerView to avoid any conflicts between the view types of added adapters. This also means each added adapter will have its own isolated pool of ViewHolders, with no re-use in between added adapters.

If your Adapters share the same view types, and can support sharing ViewHolder s between added adapters, provide an instance of Config where you set Config#isolateViewTypes to false. A common usage pattern for this is to return the R.layout.<layout_name> from the Adapter#getItemViewType(int) method.

When an added adapter calls one of the notify methods, ConcatAdapter properly offsets values before reporting it back to the RecyclerView. If an adapter calls Adapter#notifyDataSetChanged(), ConcatAdapter also calls Adapter#notifyDataSetChanged() as calling Adapter#notifyItemRangeChanged(int, int) will confuse the RecyclerView. You are highly encouraged to to use SortedList or ListAdapter to avoid calling Adapter#notifyDataSetChanged().

Whether ConcatAdapter should support stable ids is defined in the Config object. Calling Adapter#setHasStableIds(boolean) has no effect. See documentation for Config.StableIdMode for details on how to configure ConcatAdapter to use stable ids. By default, it will not use stable ids and sub adapter stable ids will be ignored. Similar to the case above, you are highly encouraged to use ListAdapter, which will automatically calculate the changes in the data set for you so you won't need stable ids.

It is common to find the adapter position of a ViewHolder to handle user action on the ViewHolder. For those cases, instead of calling ViewHolder#getAdapterPosition(), use ViewHolder#getBindingAdapterPosition(). If your adapters share ViewHolders, you can use the ViewHolder#getBindingAdapter() method to find the adapter which last bound that ViewHolder.

Summary

Nested classes
	Config The configuration object for a ConcatAdapter.

Public constructors
<init>(@NonNull vararg adapters: RecyclerView.Adapter<out RecyclerView.ViewHolder!>!) Creates a ConcatAdapter with Config#DEFAULT and the given adapters in the given order.
<init>(@NonNull config: ConcatAdapter.Config, @NonNull vararg adapters: RecyclerView.Adapter<out RecyclerView.ViewHolder!>!) Creates a ConcatAdapter with the given config and the given adapters in the given order.
<init>(@NonNull adapters: MutableList<out RecyclerView.Adapter<out RecyclerView.ViewHolder!>!>) Creates a ConcatAdapter with Config#DEFAULT and the given adapters in the given order.
<init>(@NonNull config: ConcatAdapter.Config, @NonNull adapters: MutableList<out RecyclerView.Adapter<out RecyclerView.ViewHolder!>!>) Creates a ConcatAdapter with the given config and the given adapters in the given order.

Public methods
Boolean	addAdapter(@NonNull adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder!>) Appends the given adapter to the existing list of adapters and notifies the observers of this ConcatAdapter.
Boolean	addAdapter(index: Int, @NonNull adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder!>) Adds the given adapter to the given index among other adapters that are already added.
Int	findRelativeAdapterPositionIn(@NonNull adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder!>, @NonNull viewHolder: RecyclerView.ViewHolder, globalPosition: Int) Returns the position of the given ViewHolder in the given Adapter.
MutableList<out RecyclerView.Adapter<out RecyclerView.ViewHolder!>!>	getAdapters() Returns an unmodifiable copy of the list of adapters in this ConcatAdapter.
Int	getItemCount()
Long	getItemId(position: Int)
Int	getItemViewType(position: Int)
Unit	onAttachedToRecyclerView(@NonNull recyclerView: RecyclerView)
Unit	onBindViewHolder(@NonNull holder: RecyclerView.ViewHolder, position: Int)
RecyclerView.ViewHolder	onCreateViewHolder(@NonNull parent: ViewGroup, viewType: Int)
Unit	onDetachedFromRecyclerView(@NonNull recyclerView: RecyclerView)
Boolean	onFailedToRecycleView(@NonNull holder: RecyclerView.ViewHolder)
Unit	onViewAttachedToWindow(@NonNull holder: RecyclerView.ViewHolder)
Unit	onViewDetachedFromWindow(@NonNull holder: RecyclerView.ViewHolder)
Unit	onViewRecycled(@NonNull holder: RecyclerView.ViewHolder)
Boolean	removeAdapter(@NonNull adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder!>) Removes the given adapter from the adapters list if it exists
Unit	setHasStableIds(hasStableIds: Boolean) Calling this method is an error and will result in an UnsupportedOperationException.
Unit	setStateRestorationPolicy(@NonNull strategy: RecyclerView.Adapter.StateRestorationPolicy) Calling this method is an error and will result in an UnsupportedOperationException.

Inherited functions

From class Adapter Unit bindViewHolder(@NonNull holder: VH, position: Int) This method internally calls onBindViewHolder(ViewHolder, int) to update the ViewHolder contents with the item at the given position and also sets up some private fields to be used by RecyclerView. Adapters that merge other adapters should use bindViewHolder(ViewHolder, int) when calling nested adapters so that RecyclerView can track which adapter bound the ViewHolder to return the correct position from ViewHolder#getBindingAdapterPosition() method. They should also override the findRelativeAdapterPositionIn(Adapter, ViewHolder, int) method. VH createViewHolder(@NonNull parent: ViewGroup, viewType: Int) This method calls onCreateViewHolder(ViewGroup, int) to create a new ViewHolder and initializes some private fields to be used by RecyclerView. RecyclerView.Adapter.StateRestorationPolicy getStateRestorationPolicy() Returns when this Adapter wants to restore the state. Boolean hasObservers() Returns true if one or more observers are attached to this adapter. Boolean hasStableIds() 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. If that item is relocated in the data set, the ID returned for that item should be the same. Unit notifyDataSetChanged() Notify any registered observers that the data set has changed. There are two different classes of data change events, item changes and structural changes. Item changes are when a single item has its data updated but no positional changes have occurred. Structural changes are when items are inserted, removed or moved within the data set. This event does not specify what about the data set has changed, forcing any observers to assume that all existing items and structure may no longer be valid. LayoutManagers will be forced to fully rebind and relayout all visible views. RecyclerView will attempt to synthesize visible structural change events for adapters that report that they have stable IDs when this method is used. This can help for the purposes of animation and visual object persistence but individual item views will still need to be rebound and relaid out. If you are writing an adapter it will always be more efficient to use the more specific change events if you can. Rely on notifyDataSetChanged() as a last resort. Unit notifyItemChanged(position: Int) Notify any registered observers that the item at position has changed. Equivalent to calling notifyItemChanged(position, null);. This is an item change event, not a structural change event. It indicates that any reflection of the data at position is out of date and should be updated. The item at position retains the same identity. Unit notifyItemChanged(position: Int, @Nullable payload: Any?) Notify any registered observers that the item at position has changed with an optional payload object. This is an item change event, not a structural change event. It indicates that any reflection of the data at position is out of date and should be updated. The item at position retains the same identity. Client can optionally pass a payload for partial change. These payloads will be merged and may be passed to adapter's onBindViewHolder(ViewHolder, int, List) if the item is already represented by a ViewHolder and it will be rebound to the same ViewHolder. A notifyItemRangeChanged() with null payload will clear all existing payloads on that item and prevent future payload until onBindViewHolder(ViewHolder, int, List) is called. Adapter should not assume that the payload will always be passed to onBindViewHolder(), e.g. when the view is not attached, the payload will be simply dropped. Unit notifyItemInserted(position: Int) Notify any registered observers that the item reflected at position has been newly inserted. The item previously at position is now at position position + 1. This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered. Unit notifyItemMoved(fromPosition: Int, toPosition: Int) Notify any registered observers that the item reflected at fromPosition has been moved to toPosition. This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered. Unit notifyItemRangeChanged(positionStart: Int, itemCount: Int) Notify any registered observers that the itemCount items starting at position positionStart have changed. Equivalent to calling notifyItemRangeChanged(position, itemCount, null);. This is an item change event, not a structural change event. It indicates that any reflection of the data in the given position range is out of date and should be updated. The items in the given range retain the same identity. Unit notifyItemRangeChanged(positionStart: Int, itemCount: Int, @Nullable payload: Any?) Notify any registered observers that the itemCount items starting at position positionStart have changed. An optional payload can be passed to each changed item. This is an item change event, not a structural change event. It indicates that any reflection of the data in the given position range is out of date and should be updated. The items in the given range retain the same identity. Client can optionally pass a payload for partial change. These payloads will be merged and may be passed to adapter's onBindViewHolder(ViewHolder, int, List) if the item is already represented by a ViewHolder and it will be rebound to the same ViewHolder. A notifyItemRangeChanged() with null payload will clear all existing payloads on that item and prevent future payload until onBindViewHolder(ViewHolder, int, List) is called. Adapter should not assume that the payload will always be passed to onBindViewHolder(), e.g. when the view is not attached, the payload will be simply dropped. Unit notifyItemRangeInserted(positionStart: Int, itemCount: Int) Notify any registered observers that the currently reflected itemCount items starting at positionStart have been newly inserted. The items previously located at positionStart and beyond can now be found starting at position positionStart + itemCount. This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered. 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. The items previously located at and after positionStart + itemCount may now be found at oldPosition - itemCount. This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered. Unit notifyItemRemoved(position: Int) Notify any registered observers that the item previously located at position has been removed from the data set. The items previously located at and after position may now be found at oldPosition - 1. This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered. Unit onBindViewHolder(@NonNull holder: VH, position: Int, @NonNull payloads: MutableList<Any!>) Called by RecyclerView to display the data at the specified position. This method should update the contents of the ViewHolder#itemView to reflect the item at the given position. Note that unlike android.widget.ListView, RecyclerView will not call this method again if the position of the item changes in the data set unless the item itself is invalidated or the new position cannot be determined. For this reason, you should only use the position parameter while acquiring the related data item inside this method and should not keep a copy of it. If you need the position of an item later on (e.g. in a click listener), use ViewHolder#getBindingAdapterPosition() which will have the updated adapter position. Partial bind vs full bind: The payloads parameter is a merge list from notifyItemChanged(int, Object) or notifyItemRangeChanged(int, int, Object). If the payloads list is not empty, the ViewHolder is currently bound to old data and Adapter may run an efficient partial update using the payload info. If the payload is empty, Adapter must run a full bind. Adapter should not assume that the payload passed in notify methods will be received by onBindViewHolder(). For example when the view is not attached to the screen, the payload in notifyItemChange() will be simply dropped. Unit registerAdapterDataObserver(@NonNull observer: RecyclerView.AdapterDataObserver) Register a new observer to listen for data changes. The adapter may publish a variety of events describing specific changes. Not all adapters may support all change types and some may fall back to a generic "something changed" event if more specific data is not available. Components registering observers with an adapter are responsible for unregistering those observers when finished. Unit unregisterAdapterDataObserver(@NonNull observer: RecyclerView.AdapterDataObserver) Unregister an observer currently listening for data changes. The unregistered observer will no longer receive events about changes to the adapter.

Public constructors

<init>

ConcatAdapter(@NonNull vararg adapters: RecyclerView.Adapter<out RecyclerView.ViewHolder!>!)

Creates a ConcatAdapter with Config#DEFAULT and the given adapters in the given order.

Parameters
adapters	RecyclerView.Adapter<out RecyclerView.ViewHolder!>!: The list of adapters to add

<init>

ConcatAdapter(
    @NonNull config: ConcatAdapter.Config, 
    @NonNull vararg adapters: RecyclerView.Adapter<out RecyclerView.ViewHolder!>!)

Creates a ConcatAdapter with the given config and the given adapters in the given order.

Parameters
config	ConcatAdapter.Config: The configuration for this ConcatAdapter
adapters	RecyclerView.Adapter<out RecyclerView.ViewHolder!>!: The list of adapters to add

See Also

• Config.Builder

<init>

ConcatAdapter(@NonNull adapters: MutableList<out RecyclerView.Adapter<out RecyclerView.ViewHolder!>!>)

Creates a ConcatAdapter with Config#DEFAULT and the given adapters in the given order.

Parameters
adapters	MutableList<out RecyclerView.Adapter<out RecyclerView.ViewHolder!>!>: The list of adapters to add

<init>

ConcatAdapter(
    @NonNull config: ConcatAdapter.Config, 
    @NonNull adapters: MutableList<out RecyclerView.Adapter<out RecyclerView.ViewHolder!>!>)

Creates a ConcatAdapter with the given config and the given adapters in the given order.

Parameters
config	ConcatAdapter.Config: The configuration for this ConcatAdapter
adapters	MutableList<out RecyclerView.Adapter<out RecyclerView.ViewHolder!>!>: The list of adapters to add

See Also

• Config.Builder

Public methods

addAdapter

fun addAdapter(@NonNull adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder!>): Boolean

Appends the given adapter to the existing list of adapters and notifies the observers of this ConcatAdapter.

Parameters
adapter	RecyclerView.Adapter<out RecyclerView.ViewHolder!>: The new adapter to add

Return
Boolean	true if the adapter is successfully added because it did not already exist, false otherwise.

See Also

• #addAdapter(int, Adapter)
• #removeAdapter(Adapter)

addAdapter

fun addAdapter(
    index: Int, 
    @NonNull adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder!>
): Boolean

Adds the given adapter to the given index among other adapters that are already added.

Parameters
index	Int: The index into which to insert the adapter. ConcatAdapter will throw an IndexOutOfBoundsException if the index is not between 0 and current adapter count (inclusive).
adapter	RecyclerView.Adapter<out RecyclerView.ViewHolder!>: The new adapter to add to the adapters list.

Return
Boolean	true if the adapter is successfully added because it did not already exist, false otherwise.

See Also

• #addAdapter(Adapter)
• #removeAdapter(Adapter)

findRelativeAdapterPositionIn

fun findRelativeAdapterPositionIn(
    @NonNull adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder!>, 
    @NonNull viewHolder: RecyclerView.ViewHolder, 
    globalPosition: Int
): Int

Returns the position of the given ViewHolder in the given Adapter. If the given Adapter is not part of this ConcatAdapter, RecyclerView#NO_POSITION is returned.

Parameters
adapter	RecyclerView.Adapter<out RecyclerView.ViewHolder!>: The adapter which is a sub adapter of this ConcatAdapter or itself.
viewHolder	RecyclerView.ViewHolder: The view holder whose local position in the given adapter will be returned.

Return
Int	The local position of the given ViewHolder in the given Adapter or RecyclerView#NO_POSITION if the ViewHolder is not bound to an item or the given Adapter is not part of this ConcatAdapter.

getAdapters

@NonNull fun getAdapters(): MutableList<out RecyclerView.Adapter<out RecyclerView.ViewHolder!>!>

Returns an unmodifiable copy of the list of adapters in this ConcatAdapter. Note that this is a copy hence future changes in the ConcatAdapter are not reflected in this list.

Return
MutableList<out RecyclerView.Adapter<out RecyclerView.ViewHolder!>!>	A copy of the list of adapters in this ConcatAdapter.

getItemCount

fun getItemCount(): Int

getItemId

fun getItemId(position: Int): Long

getItemViewType

fun getItemViewType(position: Int): Int

onAttachedToRecyclerView

fun onAttachedToRecyclerView(@NonNull recyclerView: RecyclerView): Unit

onBindViewHolder

fun onBindViewHolder(
    @NonNull holder: RecyclerView.ViewHolder, 
    position: Int
): Unit

onCreateViewHolder

@NonNull fun onCreateViewHolder(
    @NonNull parent: ViewGroup, 
    viewType: Int
): RecyclerView.ViewHolder

onDetachedFromRecyclerView

fun onDetachedFromRecyclerView(@NonNull recyclerView: RecyclerView): Unit

onFailedToRecycleView

fun onFailedToRecycleView(@NonNull holder: RecyclerView.ViewHolder): Boolean

onViewAttachedToWindow

fun onViewAttachedToWindow(@NonNull holder: RecyclerView.ViewHolder): Unit

onViewDetachedFromWindow

fun onViewDetachedFromWindow(@NonNull holder: RecyclerView.ViewHolder): Unit

onViewRecycled

fun onViewRecycled(@NonNull holder: RecyclerView.ViewHolder): Unit

removeAdapter

fun removeAdapter(@NonNull adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder!>): Boolean

Removes the given adapter from the adapters list if it exists

Parameters
adapter	RecyclerView.Adapter<out RecyclerView.ViewHolder!>: The adapter to remove

Return
Boolean	true if the adapter was previously added to this ConcatAdapter and now removed or false if it couldn't be found.

setHasStableIds

fun setHasStableIds(hasStableIds: Boolean): Unit

Calling this method is an error and will result in an UnsupportedOperationException. You should use the Config object passed into the ConcatAdapter to configure this behavior.

Parameters
hasStableIds	Boolean: Whether items in data set have unique identifiers or not.

setStateRestorationPolicy

fun setStateRestorationPolicy(@NonNull strategy: RecyclerView.Adapter.StateRestorationPolicy): Unit

Calling this method is an error and will result in an UnsupportedOperationException. ConcatAdapter infers this value from added Adapters.

Parameters
strategy	RecyclerView.Adapter.StateRestorationPolicy: The saved state restoration strategy for this Adapter such that ConcatAdapter will allow state restoration only if all added adapters allow it or there are no adapters.