PagerAdapter

Kotlin |Java

abstract class PagerAdapter

kotlin.Any
↳	androidx.viewpager.widget.PagerAdapter

Known Direct Subclasses

FragmentPagerAdapter, FragmentStatePagerAdapter

FragmentPagerAdapter	Implementation of `PagerAdapter` that represents each page as a `Fragment` that is persistently kept in the fragment manager as long as the user can return to the page.
FragmentStatePagerAdapter	Implementation of `PagerAdapter` that uses a `Fragment` to manage each page.

Base class providing the adapter to populate pages inside of a ViewPager. You will most likely want to use a more specific implementation of this, such as androidx.fragment.app.FragmentPagerAdapter or androidx.fragment.app.FragmentStatePagerAdapter.

When you implement a PagerAdapter, you must override the following methods at minimum:

instantiateItem(ViewGroup, int)
destroyItem(ViewGroup, int, Object)
getCount()
isViewFromObject(View, Object)

PagerAdapter is more general than the adapters used for AdapterViews. Instead of providing a View recycling mechanism directly ViewPager uses callbacks to indicate the steps taken during an update. A PagerAdapter may implement a form of View recycling if desired or use a more sophisticated method of managing page Views such as Fragment transactions where each page is represented by its own Fragment.

ViewPager associates each page with a key Object instead of working with Views directly. This key is used to track and uniquely identify a given page independent of its position in the adapter. A call to the PagerAdapter method startUpdate(ViewGroup) indicates that the contents of the ViewPager are about to change. One or more calls to instantiateItem(ViewGroup, int) and/or destroyItem(ViewGroup, int, Object) will follow, and the end of an update will be signaled by a call to finishUpdate(ViewGroup). By the time finishUpdate returns the views associated with the key objects returned by instantiateItem should be added to the parent ViewGroup passed to these methods and the views associated with the keys passed to destroyItem should be removed. The method isViewFromObject(View, Object) identifies whether a page View is associated with a given key object.

A very simple PagerAdapter may choose to use the page Views themselves as key objects, returning them from instantiateItem(ViewGroup, int) after creation and adding them to the parent ViewGroup. A matching destroyItem(ViewGroup, int, Object) implementation would remove the View from the parent ViewGroup and isViewFromObject(View, Object) could be implemented as return view == object;.

PagerAdapter supports data set changes. Data set changes must occur on the main thread and must end with a call to notifyDataSetChanged() similar to AdapterView adapters derived from android.widget.BaseAdapter. A data set change may involve pages being added, removed, or changing position. The ViewPager will keep the current page active provided the adapter implements the method getItemPosition(Object).

Summary

Constants
static Int	`POSITION_NONE`
static Int	`POSITION_UNCHANGED`

Public constructors
`<init>()` Base class providing the adapter to populate pages inside of a `ViewPager`.

Public methods
open Unit	`destroyItem(@NonNull container: ViewGroup, position: Int, @NonNull object: Any)` Remove a page for the given position.
open Unit	`destroyItem(@NonNull container: View, position: Int, @NonNull object: Any)` Remove a page for the given position.
open Unit	`finishUpdate(@NonNull container: ViewGroup)` Called when the a change in the shown pages has been completed.
open Unit	`finishUpdate(@NonNull container: View)` Called when the a change in the shown pages has been completed.
abstract Int	`getCount()` Return the number of views available.
open Int	`getItemPosition(@NonNull object: Any)` Called when the host view is attempting to determine if an item's position has changed.
open CharSequence?	`getPageTitle(position: Int)` This method may be called by the ViewPager to obtain a title string to describe the specified page.
open 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]
open Any	`instantiateItem(@NonNull container: ViewGroup, position: Int)` Create the page for the given position.
open Any	`instantiateItem(@NonNull container: View, position: Int)` Create the page for the given position.
abstract Boolean	`isViewFromObject(@NonNull view: View, @NonNull object: Any)` Determines whether a page View is associated with a specific key object as returned by `instantiateItem(ViewGroup, int)`.
open Unit	`notifyDataSetChanged()` This method should be called by the application if the data backing this adapter has changed and associated views should update.
open Unit	`registerDataSetObserver(@NonNull observer: DataSetObserver)` Register an observer to receive callbacks related to the adapter's data changing.
open Unit	`restoreState(@Nullable state: Parcelable?, @Nullable loader: ClassLoader?)` Restore any instance state associated with this adapter and its pages that was previously saved by `saveState()`.
open Parcelable?	`saveState()` Save any instance state associated with this adapter and its pages that should be restored if the current UI state needs to be reconstructed.
open Unit	`setPrimaryItem(@NonNull container: ViewGroup, 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.
open 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.
open Unit	`startUpdate(@NonNull container: ViewGroup)` Called when a change in the shown pages is going to start being made.
open Unit	`startUpdate(@NonNull container: View)` Called when a change in the shown pages is going to start being made.
open Unit	`unregisterDataSetObserver(@NonNull observer: DataSetObserver)` Unregister an observer from callbacks related to the adapter's data changing.

Constants

POSITION_NONE

static val POSITION_NONE: Int

Value: -2

POSITION_UNCHANGED

static val POSITION_UNCHANGED: Int

Value: -1

Public constructors

<init>

PagerAdapter()

When you implement a PagerAdapter, you must override the following methods at minimum:

instantiateItem(ViewGroup, int)
destroyItem(ViewGroup, int, Object)
getCount()
isViewFromObject(View, Object)