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