PagerAdapter

abstract class PagerAdapter

Known direct subclasses

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:

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 indicates that the contents of the ViewPager are about to change. One or more calls to instantiateItem and/or destroyItem will follow, and the end of an update will be signaled by a call to finishUpdate. 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 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 after creation and adding them to the parent ViewGroup. A matching destroyItem implementation would remove the View from the parent ViewGroup and isViewFromObject 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.

Summary

Constants
const Int
const Int

Public constructors

Public functions
Unit
destroyItem(container: View, position: Int, object: Any)

This function is deprecated.

Use destroyItem
Unit
destroyItem(container: ViewGroup, position: Int, object: Any)

Remove a page for the given position.
Unit
finishUpdate(container: View)

This function is deprecated.

Use finishUpdate
Unit
finishUpdate(container: ViewGroup)

Called when the a change in the shown pages has been completed.
abstract Int

Return the number of views available.
Int

Called when the host view is attempting to determine if an item's position has changed.
CharSequence?
getPageTitle(position: Int)

This method may be called by the ViewPager to obtain a title string to describe the specified page.
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(container: View, position: Int)

This function is deprecated.

Use instantiateItem
Any
instantiateItem(container: ViewGroup, position: Int)

Create the page for the given position.
abstract Boolean
isViewFromObject(view: View, object: Any)

Determines whether a page View is associated with a specific key object as returned by instantiateItem.
Unit

This method should be called by the application if the data backing this adapter has changed and associated views should update.
Unit

Register an observer to receive callbacks related to the adapter's data changing.
Unit
restoreState(state: Parcelable?, loader: ClassLoader?)

Restore any instance state associated with this adapter and its pages that was previously saved by saveState.
Parcelable?

Save any instance state associated with this adapter and its pages that should be restored if the current UI state needs to be reconstructed.
Unit
setPrimaryItem(container: View, position: Int, object: Any)

This function is deprecated.

Use setPrimaryItem
Unit
setPrimaryItem(container: ViewGroup, position: Int, 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(container: View)

This function is deprecated.

Use startUpdate
Unit
startUpdate(container: ViewGroup)

Called when a change in the shown pages is going to start being made.
Unit

Unregister an observer from callbacks related to the adapter's data changing.

Constants

POSITION_NONE

Added in 1.1.0
const val POSITION_NONE = -2: Int

POSITION_UNCHANGED

Added in 1.1.0
const val POSITION_UNCHANGED = -1: Int

Public constructors

PagerAdapter

Added in 1.1.0
PagerAdapter()

Public functions

destroyItem

Added in 1.1.0
Deprecated in 1.1.0
fun destroyItem(container: View, position: Int, object: Any): Unit

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.

Parameters
container: View

The containing View from which the page will be removed.
position: Int

The page position to be removed.
object: Any

The same object that was returned by instantiateItem.

destroyItem

Added in 1.1.0
fun destroyItem(container: ViewGroup, position: Int, object: Any): Unit

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.

Parameters
container: ViewGroup

The containing View from which the page will be removed.
position: Int

The page position to be removed.
object: Any

The same object that was returned by instantiateItem.

finishUpdate

Added in 1.1.0
Deprecated in 1.1.0
fun finishUpdate(container: View): Unit

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.

Parameters
container: View

The containing View which is displaying this adapter's page views.

finishUpdate

Added in 1.1.0
fun finishUpdate(container: ViewGroup): Unit

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.

Parameters
container: ViewGroup

The containing View which is displaying this adapter's page views.

getCount

Added in 1.1.0
abstract fun getCount(): Int

Return the number of views available.

getItemPosition

Added in 1.1.0
fun getItemPosition(object: Any): Int

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.

Parameters
object: Any

Object representing an item, previously returned by a call to instantiateItem.
Returns
Int

object's new position index from [0, getCount), POSITION_UNCHANGED if the object's position has not changed, or POSITION_NONE if the item is no longer present.

getPageTitle

Added in 1.1.0
fun getPageTitle(position: Int): CharSequence?

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.

Parameters
position: Int

The position of the title requested
Returns
CharSequence?

A title for the requested page

getPageWidth

Added in 1.1.0
fun getPageWidth(position: Int): Float

Returns the proportional width of a given page as a percentage of the ViewPager's measured width from (0.f-1.f]

Parameters
position: Int

The position of the page requested
Returns
Float

Proportional width for the given page position

instantiateItem

Added in 1.1.0
Deprecated in 1.1.0
fun instantiateItem(container: View, position: Int): Any

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.

Parameters
container: View

The containing View in which the page will be shown.
position: Int

The page position to be instantiated.
Returns
Any

Returns an Object representing the new page. This does not need to be a View, but can be some other container of the page.

instantiateItem

Added in 1.1.0
fun instantiateItem(container: ViewGroup, position: Int): Any

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.

Parameters
container: ViewGroup

The containing View in which the page will be shown.
position: Int

The page position to be instantiated.
Returns
Any

Returns an Object representing the new page. This does not need to be a View, but can be some other container of the page.

isViewFromObject

Added in 1.1.0
abstract fun isViewFromObject(view: View, object: Any): Boolean

Determines whether a page View is associated with a specific key object as returned by instantiateItem. This method is required for a PagerAdapter to function properly.

Parameters
view: View

Page View to check for association with object
object: Any

Object to check for association with view
Returns
Boolean

true if view is associated with the key object object

notifyDataSetChanged

Added in 1.1.0
fun notifyDataSetChanged(): Unit

This method should be called by the application if the data backing this adapter has changed and associated views should update.

registerDataSetObserver

Added in 1.1.0
fun registerDataSetObserver(observer: DataSetObserver): Unit

Register an observer to receive callbacks related to the adapter's data changing.

Parameters
observer: DataSetObserver

The android.database.DataSetObserver which will receive callbacks.

restoreState

Added in 1.1.0
fun restoreState(state: Parcelable?, loader: ClassLoader?): Unit

Restore any instance state associated with this adapter and its pages that was previously saved by saveState.

Parameters
state: Parcelable?

State previously saved by a call to saveState
loader: ClassLoader?

A ClassLoader that should be used to instantiate any restored objects

saveState

Added in 1.1.0
fun saveState(): Parcelable?

Save any instance state associated with this adapter and its pages that should be restored if the current UI state needs to be reconstructed.

Returns
Parcelable?

Saved state for this adapter

setPrimaryItem

Added in 1.1.0
Deprecated in 1.1.0
fun setPrimaryItem(container: View, position: Int, object: Any): Unit

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.

Parameters
container: View

The containing View from which the page will be removed.
position: Int

The page position that is now the primary.
object: Any

The same object that was returned by instantiateItem.

setPrimaryItem

Added in 1.1.0
fun setPrimaryItem(container: ViewGroup, position: Int, object: Any): Unit

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. This method will not be invoked when the adapter contains no items.

Parameters
container: ViewGroup

The containing View from which the page will be removed.
position: Int

The page position that is now the primary.
object: Any

The same object that was returned by instantiateItem.

startUpdate

Added in 1.1.0
Deprecated in 1.1.0
fun startUpdate(container: View): Unit

Called when a change in the shown pages is going to start being made.

Parameters
container: View

The containing View which is displaying this adapter's page views.

startUpdate

Added in 1.1.0
fun startUpdate(container: ViewGroup): Unit

Called when a change in the shown pages is going to start being made.

Parameters
container: ViewGroup

The containing View which is displaying this adapter's page views.

unregisterDataSetObserver

Added in 1.1.0
fun unregisterDataSetObserver(observer: DataSetObserver): Unit

Unregister an observer from callbacks related to the adapter's data changing.

Parameters
observer: DataSetObserver

The android.database.DataSetObserver which will be unregistered.