FragmentStateAdapter

Kotlin |Java

abstract class FragmentStateAdapter : RecyclerView.Adapter<FragmentViewHolder!>, StatefulAdapter

kotlin.Any
↳	androidx.recyclerview.widget.RecyclerView.Adapter<androidx.viewpager2.adapter.FragmentViewHolder>
	↳	androidx.viewpager2.adapter.FragmentStateAdapter

Similar in behavior to FragmentStatePagerAdapter

Lifecycle within RecyclerView:

RecyclerView.ViewHolder initially an empty FrameLayout, serves as a re-usable container for a Fragment in later stages.
RecyclerView.Adapter#onBindViewHolder we ask for a Fragment for the position. If we already have the fragment, or have previously saved its state, we use those.
RecyclerView.Adapter#onAttachedToWindow we attach the Fragment to a container.
RecyclerView.Adapter#onViewRecycled we remove, save state, destroy the Fragment.

Summary

Nested classes
abstract	`FragmentTransactionCallback` Callback interface for listening to fragment lifecycle changes that happen inside the adapter.

Public constructors
`<init>(@NonNull fragmentActivity: FragmentActivity)`
`<init>(@NonNull fragment: Fragment)`
`<init>(@NonNull fragmentManager: FragmentManager, @NonNull lifecycle: Lifecycle)`

Public methods
open Boolean	`containsItem(itemId: Long)` Default implementation works for collections that don't add, move, remove items.
abstract Fragment	`createFragment(position: Int)` Provide a new Fragment associated with the specified position.
open Long	`getItemId(position: Int)` Default implementation works for collections that don't add, move, remove items.
open Unit	`onAttachedToRecyclerView(@NonNull recyclerView: RecyclerView)`
Unit	`onBindViewHolder(@NonNull holder: FragmentViewHolder, position: Int)`
FragmentViewHolder	`onCreateViewHolder(@NonNull parent: ViewGroup, viewType: Int)`
open Unit	`onDetachedFromRecyclerView(@NonNull recyclerView: RecyclerView)`
Boolean	`onFailedToRecycleView(@NonNull holder: FragmentViewHolder)`
Unit	`onViewAttachedToWindow(@NonNull holder: FragmentViewHolder)`
Unit	`onViewRecycled(@NonNull holder: FragmentViewHolder)`
open Unit	`registerFragmentTransactionCallback(@NonNull callback: FragmentStateAdapter.FragmentTransactionCallback)` Registers a `FragmentTransactionCallback` to listen to fragment lifecycle changes that happen inside the adapter.
Unit	`restoreState(@NonNull savedState: Parcelable)`
Parcelable	`saveState()`
Unit	`setHasStableIds(hasStableIds: Boolean)`
open Unit	`unregisterFragmentTransactionCallback(@NonNull callback: FragmentStateAdapter.FragmentTransactionCallback)` Unregisters a `FragmentTransactionCallback`.

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.
`Int`	`findRelativeAdapterPositionIn(@NonNull adapter: RecyclerView.Adapter<out RecyclerView.ViewHolder!>, @NonNull viewHolder: RecyclerView.ViewHolder, localPosition: Int)` Returns the position of the given `ViewHolder` in the given `Adapter`. If the given `Adapter` is not part of this `Adapter`, `RecyclerView#NO_POSITION` is returned.
`Int`	`getItemCount()` Returns the total number of items in the data set held by the adapter.
`Int`	`getItemViewType(position: Int)` Return the view type of the item at `position` for the purposes of view recycling. The default implementation of this method returns 0, making the assumption of a single view type for the adapter. Unlike ListView adapters, types need not be contiguous. Consider using id resources to uniquely identify item view types.
`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`	`onViewDetachedFromWindow(@NonNull holder: VH)` Called when a view created by this adapter has been detached from its window. Becoming detached from the window is not necessarily a permanent condition; the consumer of an Adapter's views may choose to cache views offscreen while they are not visible, attaching and detaching them as appropriate.
`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`	`setStateRestorationPolicy(@NonNull strategy: RecyclerView.Adapter.StateRestorationPolicy)` Sets the state restoration strategy for the Adapter. By default, it is set to `StateRestorationPolicy#ALLOW` which means RecyclerView expects any set Adapter to be immediately capable of restoring the RecyclerView's saved scroll position. This behaviour might be undesired if the Adapter's data is loaded asynchronously, and thus unavailable during initial layout (e.g. after Activity rotation). To avoid losing scroll position, you can change this to be either `StateRestorationPolicy#PREVENT_WHEN_EMPTY` or `StateRestorationPolicy#PREVENT`. Note that the former means your RecyclerView will restore state as soon as Adapter has 1 or more items while the latter requires you to call `setStateRestorationPolicy(StateRestorationPolicy)` with either `StateRestorationPolicy#ALLOW` or `StateRestorationPolicy#PREVENT_WHEN_EMPTY` again when the Adapter is ready to restore its state. RecyclerView will still layout even when State restoration is disabled. The behavior of how State is restored is up to the `LayoutManager`. All default LayoutManagers will override current state with restored state when state restoration happens (unless an explicit call to `LayoutManager#scrollToPosition(int)` is made). Calling this method after state is restored will not have any effect other than changing the return value of `getStateRestorationPolicy()`.
`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>

FragmentStateAdapter(@NonNull fragmentActivity: FragmentActivity)

Parameters
`fragmentActivity`	FragmentActivity: if the `ViewPager2` lives directly in a `FragmentActivity` subclass.

See Also

FragmentStateAdapter#FragmentStateAdapter(Fragment)
FragmentStateAdapter#FragmentStateAdapter(FragmentManager, Lifecycle)

<init>

FragmentStateAdapter(@NonNull fragment: Fragment)

Parameters
`fragment`	Fragment: if the `ViewPager2` lives directly in a `Fragment` subclass.

See Also

FragmentStateAdapter#FragmentStateAdapter(FragmentActivity)
FragmentStateAdapter#FragmentStateAdapter(FragmentManager, Lifecycle)

<init>

FragmentStateAdapter(
    @NonNull fragmentManager: FragmentManager, 
    @NonNull lifecycle: Lifecycle)

Parameters
`fragmentManager`	FragmentManager: of `ViewPager2`'s host
`lifecycle`	Lifecycle: of `ViewPager2`'s host

See Also

FragmentStateAdapter#FragmentStateAdapter(FragmentActivity)
FragmentStateAdapter#FragmentStateAdapter(Fragment)

Public methods

containsItem

open fun containsItem(itemId: Long): Boolean

Default implementation works for collections that don't add, move, remove items.

When overriding, also override getItemId(int)

createFragment

@NonNull abstract fun createFragment(position: Int): Fragment

Provide a new Fragment associated with the specified position.

The adapter will be responsible for the Fragment lifecycle:

The Fragment will be used to display an item.
The Fragment will be destroyed when it gets too far from the viewport, and its state will be saved. When the item is close to the viewport again, a new Fragment will be requested, and a previously saved state will be used to initialize it.

See Also

ViewPager2#setOffscreenPageLimit

getItemId

open fun getItemId(position: Int): Long

Default implementation works for collections that don't add, move, remove items.

When overriding, also override containsItem(long).

If the item is not a part of the collection, return RecyclerView#NO_ID.

Parameters
`position`	Int: Adapter position

Return
`Long`	stable item id `RecyclerView.Adapter#hasStableIds()`

onAttachedToRecyclerView

@CallSuper open fun onAttachedToRecyclerView(@NonNull recyclerView: RecyclerView): Unit

onBindViewHolder

fun onBindViewHolder(
    @NonNull holder: FragmentViewHolder, 
    position: Int
): Unit

onCreateViewHolder

@NonNull fun onCreateViewHolder(
    @NonNull parent: ViewGroup, 
    viewType: Int
): FragmentViewHolder

onDetachedFromRecyclerView

@CallSuper open fun onDetachedFromRecyclerView(@NonNull recyclerView: RecyclerView): Unit

onFailedToRecycleView

fun onFailedToRecycleView(@NonNull holder: FragmentViewHolder): Boolean

onViewAttachedToWindow

fun onViewAttachedToWindow(@NonNull holder: FragmentViewHolder): Unit

onViewRecycled

fun onViewRecycled(@NonNull holder: FragmentViewHolder): Unit

registerFragmentTransactionCallback

open fun registerFragmentTransactionCallback(@NonNull callback: FragmentStateAdapter.FragmentTransactionCallback): Unit

Registers a FragmentTransactionCallback to listen to fragment lifecycle changes that happen inside the adapter.

Parameters
`callback`	FragmentStateAdapter.FragmentTransactionCallback: Callback to register

restoreState

fun restoreState(@NonNull savedState: Parcelable): Unit

saveState

@NonNull fun saveState(): Parcelable

setHasStableIds

fun setHasStableIds(hasStableIds: Boolean): Unit

unregisterFragmentTransactionCallback

open fun unregisterFragmentTransactionCallback(@NonNull callback: FragmentStateAdapter.FragmentTransactionCallback): Unit

Unregisters a FragmentTransactionCallback.

Parameters
`callback`	FragmentStateAdapter.FragmentTransactionCallback: Callback to unregister

See Also

#registerFragmentTransactionCallback