FragmentStatePagerAdapter

Kotlin |Java

abstract class FragmentStatePagerAdapter : PagerAdapter

kotlin.Any
↳	androidx.viewpager.widget.PagerAdapter
	↳	androidx.fragment.app.FragmentStatePagerAdapter

Implementation of PagerAdapter that uses a Fragment to manage each page. This class also handles saving and restoring of fragment's state.

This version of the pager is more useful when there are a large number of pages, working more like a list view. When pages are not visible to the user, their entire fragment may be destroyed, only keeping the saved state of that fragment. This allows the pager to hold on to much less memory associated with each visited page as compared to FragmentPagerAdapter at the cost of potentially more overhead when switching between pages.

When using FragmentPagerAdapter the host ViewPager must have a valid ID set.

Subclasses only need to implement getItem(int) and getCount() to have a working adapter.

Here is an example implementation of a pager containing fragments of lists:

The R.layout.fragment_pager resource of the top-level fragment is:

The R.layout.fragment_pager_list resource containing each individual fragment's layout is:

Summary

Constants
static Int	BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT Indicates that only the current fragment will be in the Lifecycle.State#RESUMED state.
static Int	BEHAVIOR_SET_USER_VISIBLE_HINT Indicates that Fragment#setUserVisibleHint(boolean) will be called when the current fragment changes.

Inherited constants
From class PagerAdapter Int POSITION_NONE Int POSITION_UNCHANGED

Public constructors
<init>(@NonNull fm: FragmentManager) Constructor for FragmentStatePagerAdapter that sets the fragment manager for the adapter.
<init>(@NonNull fm: FragmentManager, behavior: Int) Constructor for FragmentStatePagerAdapter.

Public methods
open Unit	destroyItem(@NonNull container: ViewGroup, position: Int, @NonNull object: Any)
open Unit	finishUpdate(@NonNull container: ViewGroup)
abstract Fragment	getItem(position: Int) Return the Fragment associated with a specified position.
open Any	instantiateItem(@NonNull container: ViewGroup, position: Int)
open Boolean	isViewFromObject(@NonNull view: View, @NonNull object: Any)
open Unit	restoreState(@Nullable state: Parcelable?, @Nullable loader: ClassLoader?)
open Parcelable?	saveState()
open Unit	setPrimaryItem(@NonNull container: ViewGroup, position: Int, @NonNull object: Any)
open Unit	startUpdate(@NonNull container: ViewGroup)

Inherited functions

From class PagerAdapter Unit destroyItem(@NonNull container: View, position: Int, @NonNull object: Any) Remove a page for the given position. The adapter is responsible for removing the view from its container, although it only must ensure this is done by the time it returns from finishUpdate(View). Unit finishUpdate(@NonNull container: View) Called when the a change in the shown pages has been completed. At this point you must ensure that all of the pages have actually been added or removed from the container as appropriate. Int getCount() Return the number of views available. Int getItemPosition(@NonNull object: Any) Called when the host view is attempting to determine if an item's position has changed. Returns POSITION_UNCHANGED if the position of the given item has not changed or POSITION_NONE if the item is no longer present in the adapter. The default implementation assumes that items will never change position and always returns POSITION_UNCHANGED. CharSequence? getPageTitle(position: Int) This method may be called by the ViewPager to obtain a title string to describe the specified page. This method may return null indicating no title for this page. The default implementation returns null. Float getPageWidth(position: Int) Returns the proportional width of a given page as a percentage of the ViewPager's measured width from (0.f-1.f] Any instantiateItem(@NonNull container: View, position: Int) Create the page for the given position. The adapter is responsible for adding the view to the container given here, although it only must ensure this is done by the time it returns from finishUpdate(ViewGroup). Unit notifyDataSetChanged() This method should be called by the application if the data backing this adapter has changed and associated views should update. Unit registerDataSetObserver(@NonNull observer: DataSetObserver) Register an observer to receive callbacks related to the adapter's data changing. Unit setPrimaryItem(@NonNull container: View, position: Int, @NonNull object: Any) Called to inform the adapter of which item is currently considered to be the "primary", that is the one show to the user as the current page. Unit startUpdate(@NonNull container: View) Called when a change in the shown pages is going to start being made. Unit unregisterDataSetObserver(@NonNull observer: DataSetObserver) Unregister an observer from callbacks related to the adapter's data changing.

Constants

BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT

static val BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT: Int

Indicates that only the current fragment will be in the Lifecycle.State#RESUMED state. All other Fragments are capped at Lifecycle.State#STARTED.

Value: 1

See Also

• #FragmentStatePagerAdapter(FragmentManager, int)

BEHAVIOR_SET_USER_VISIBLE_HINT

static val BEHAVIOR_SET_USER_VISIBLE_HINT: Int

Deprecated: This behavior relies on the deprecated Fragment#setUserVisibleHint(boolean) API. Use BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT to switch to its replacement, FragmentTransaction#setMaxLifecycle.

Indicates that Fragment#setUserVisibleHint(boolean) will be called when the current fragment changes.

Value: 0

See Also

• #FragmentStatePagerAdapter(FragmentManager, int)

Public constructors

<init>

FragmentStatePagerAdapter(@NonNull fm: FragmentManager)

Deprecated: use FragmentStatePagerAdapter(FragmentManager, int) with BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT

Constructor for FragmentStatePagerAdapter that sets the fragment manager for the adapter. This is the equivalent of calling FragmentStatePagerAdapter(FragmentManager, int) and passing in BEHAVIOR_SET_USER_VISIBLE_HINT.

Fragments will have Fragment#setUserVisibleHint(boolean) called whenever the current Fragment changes.

Parameters
fm	FragmentManager: fragment manager that will interact with this adapter

<init>

FragmentStatePagerAdapter(
    @NonNull fm: FragmentManager, 
    behavior: Int)

Constructor for FragmentStatePagerAdapter. If BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT is passed in, then only the current Fragment is in the Lifecycle.State#RESUMED state, while all other fragments are capped at Lifecycle.State#STARTED. If BEHAVIOR_SET_USER_VISIBLE_HINT is passed, all fragments are in the Lifecycle.State#RESUMED state and there will be callbacks to Fragment#setUserVisibleHint(boolean).

Parameters
fm	FragmentManager: fragment manager that will interact with this adapter
behavior	Int: determines if only current fragments are in a resumed state

Public methods

destroyItem

open fun destroyItem(
    @NonNull container: ViewGroup, 
    position: Int, 
    @NonNull object: Any
): Unit

finishUpdate

open fun finishUpdate(@NonNull container: ViewGroup): Unit

getItem

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

Return the Fragment associated with a specified position.

instantiateItem

@NonNull open fun instantiateItem(
    @NonNull container: ViewGroup, 
    position: Int
): Any

isViewFromObject

open fun isViewFromObject(
    @NonNull view: View, 
    @NonNull object: Any
): Boolean

restoreState

open fun restoreState(
    @Nullable state: Parcelable?, 
    @Nullable loader: ClassLoader?
): Unit

saveState

@Nullable open fun saveState(): Parcelable?

setPrimaryItem

open fun setPrimaryItem(
    @NonNull container: ViewGroup, 
    position: Int, 
    @NonNull object: Any
): Unit

startUpdate

open fun startUpdate(@NonNull container: ViewGroup): Unit