FragmentStateAdapter

fun containsItem(itemId: Long): Boolean

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

When overriding, also override getItemId

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.

fun getItemId(position: Int): Long

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

When overriding, also override containsItem.

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

@CallSuper
fun onAttachedToRecyclerView(recyclerView: RecyclerView): Unit

Called by RecyclerView when it starts observing this Adapter.

Keep in mind that same adapter may be observed by multiple RecyclerViews.

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

Called by RecyclerView to display the data at the specified position. This method should update the contents of the 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 getBindingAdapterPosition which will have the updated adapter position. Override onBindViewHolder instead if Adapter can handle efficient partial bind.

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

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

This new ViewHolder should be constructed with a new View that can represent the items of the given type. You can either create a new View manually or inflate it from an XML layout file.

The new ViewHolder will be used to display items of the adapter using onBindViewHolder. Since it will be re-used to display different items in the data set, it is a good idea to cache references to sub views of the View to avoid unnecessary findViewById calls.

@CallSuper
fun onDetachedFromRecyclerView(recyclerView: RecyclerView): Unit

Called by RecyclerView when it stops observing this Adapter.

fun onFailedToRecycleView(holder: FragmentViewHolder): Boolean

Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled due to its transient state. Upon receiving this callback, Adapter can clear the animation(s) that effect the View's transient state and return true so that the View can be recycled. Keep in mind that the View in question is already removed from the RecyclerView.

In some cases, it is acceptable to recycle a View although it has transient state. Most of the time, this is a case where the transient state will be cleared in onBindViewHolder call when View is rebound to a new position. For this reason, RecyclerView leaves the decision to the Adapter and uses the return value of this method to decide whether the View should be recycled or not.

Note that when all animations are created by RecyclerView.ItemAnimator, you should never receive this callback because RecyclerView keeps those Views as children until their animations are complete. This callback is useful when children of the item views create animations which may not be easy to implement using an ItemAnimator.

You should never fix this issue by calling holder.itemView.setHasTransientState(false); unless you've previously called holder.itemView.setHasTransientState(true);. Each View.setHasTransientState(true) call must be matched by a View.setHasTransientState(false) call, otherwise, the state of the View may become inconsistent. You should always prefer to end or cancel animations that are triggering the transient state instead of handling it manually.

fun onViewAttachedToWindow(holder: FragmentViewHolder): Unit

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

This can be used as a reasonable signal that the view is about to be seen by the user. If the adapter previously freed any resources in onViewDetachedFromWindow those resources should be restored here.

fun onViewRecycled(holder: FragmentViewHolder): Unit

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

A view is recycled when a LayoutManager decides that it no longer needs to be attached to its parent RecyclerView. This can be because it has fallen out of visibility or a set of cached views represented by views still attached to the parent RecyclerView. If an item view has large or expensive data bound to it such as large bitmaps, this may be a good place to release those resources.

RecyclerView calls this method right before clearing ViewHolder's internal data and sending it to RecycledViewPool. This way, if ViewHolder was holding valid information before being recycled, you can call getBindingAdapterPosition to get its adapter position.

fun registerFragmentTransactionCallback(
    callback: FragmentStateAdapter.FragmentTransactionCallback
): Unit

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

fun restoreState(savedState: Parcelable): Unit

Restores adapter state

fun saveState(): Parcelable

Saves adapter state

fun setHasStableIds(hasStableIds: Boolean): Unit

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

fun unregisterFragmentTransactionCallback(
    callback: FragmentStateAdapter.FragmentTransactionCallback
): Unit

Unregisters a FragmentTransactionCallback.