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PagerAdapter

public 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
static final int
static final int

Public constructors

Public methods
void
destroyItem(@NonNull View container, int position, @NonNull Object object)

This method is deprecated.

Use destroyItem
void
destroyItem(
    @NonNull ViewGroup container,
    int position,
    @NonNull Object object
)

Remove a page for the given position.
void

This method is deprecated.

Use finishUpdate
void

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.
@Nullable CharSequence
getPageTitle(int position)

This method may be called by the ViewPager to obtain a title string to describe the specified page.
float
getPageWidth(int position)

Returns the proportional width of a given page as a percentage of the ViewPager's measured width from (0.f-1.f]
@NonNull Object
instantiateItem(@NonNull View container, int position)

This method is deprecated.

Use instantiateItem
@NonNull Object
instantiateItem(@NonNull ViewGroup container, int position)

Create the page for the given position.
abstract boolean

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

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

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

Restore any instance state associated with this adapter and its pages that was previously saved by saveState.
@Nullable 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.
void
setPrimaryItem(
    @NonNull View container,
    int position,
    @NonNull Object object
)

This method is deprecated.

Use setPrimaryItem
void
setPrimaryItem(
    @NonNull ViewGroup container,
    int position,
    @NonNull Object object
)

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.
void
startUpdate(@NonNull View container)

This method is deprecated.

Use startUpdate
void

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

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

Constants

POSITION_NONE

Added in 1.1.0
public static final int POSITION_NONE = -2

POSITION_UNCHANGED

Added in 1.1.0
public static final int POSITION_UNCHANGED = -1

Public constructors

PagerAdapter

Added in 1.1.0
public PagerAdapter()

Public methods

destroyItem

Added in 1.1.0
Deprecated in 1.1.0
public void destroyItem(@NonNull View container, int position, @NonNull Object object)

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
@NonNull View container

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

The page position to be removed.
@NonNull Object object

The same object that was returned by instantiateItem.

destroyItem

Added in 1.1.0
public void destroyItem(
    @NonNull ViewGroup container,
    int position,
    @NonNull Object object
)

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
@NonNull ViewGroup container

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

The page position to be removed.
@NonNull Object object

The same object that was returned by instantiateItem.

finishUpdate

Added in 1.1.0
Deprecated in 1.1.0
public void finishUpdate(@NonNull View container)

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
@NonNull View container

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

finishUpdate

Added in 1.1.0
public void finishUpdate(@NonNull ViewGroup container)

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
@NonNull ViewGroup container

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

getCount

Added in 1.1.0
public abstract int getCount()

Return the number of views available.

getItemPosition

Added in 1.1.0
public int getItemPosition(@NonNull Object object)

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
@NonNull Object object

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
public @Nullable CharSequence getPageTitle(int position)

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
int position

The position of the title requested
Returns
@Nullable CharSequence

A title for the requested page

getPageWidth

Added in 1.1.0
public float getPageWidth(int position)

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

Parameters
int position

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
public @NonNull Object instantiateItem(@NonNull View container, int position)

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
@NonNull View container

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

The page position to be instantiated.
Returns
@NonNull Object

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
public @NonNull Object instantiateItem(@NonNull ViewGroup container, int position)

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
@NonNull ViewGroup container

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

The page position to be instantiated.
Returns
@NonNull Object

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
public abstract boolean isViewFromObject(@NonNull View view, @NonNull Object object)

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
@NonNull View view

Page View to check for association with object
@NonNull Object object

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
public void notifyDataSetChanged()

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
public void registerDataSetObserver(@NonNull DataSetObserver observer)

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

Parameters
@NonNull DataSetObserver observer

The android.database.DataSetObserver which will receive callbacks.

restoreState

Added in 1.1.0
public void restoreState(@Nullable Parcelable state, @Nullable ClassLoader loader)

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

Parameters
@Nullable Parcelable state

State previously saved by a call to saveState
@Nullable ClassLoader loader

A ClassLoader that should be used to instantiate any restored objects

saveState

Added in 1.1.0
public @Nullable 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.

Returns
@Nullable Parcelable

Saved state for this adapter

setPrimaryItem

Added in 1.1.0
Deprecated in 1.1.0
public void setPrimaryItem(
    @NonNull View container,
    int position,
    @NonNull Object object
)

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
@NonNull View container

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

The page position that is now the primary.
@NonNull Object object

The same object that was returned by instantiateItem.

setPrimaryItem

Added in 1.1.0
public void setPrimaryItem(
    @NonNull ViewGroup container,
    int position,
    @NonNull Object object
)

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
@NonNull ViewGroup container

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

The page position that is now the primary.
@NonNull Object object

The same object that was returned by instantiateItem.

startUpdate

Added in 1.1.0
Deprecated in 1.1.0
public void startUpdate(@NonNull View container)

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

Parameters
@NonNull View container

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

startUpdate

Added in 1.1.0
public void startUpdate(@NonNull ViewGroup container)

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

Parameters
@NonNull ViewGroup container

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

unregisterDataSetObserver

Added in 1.1.0
public void unregisterDataSetObserver(@NonNull DataSetObserver observer)

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

Parameters
@NonNull DataSetObserver observer

The android.database.DataSetObserver which will be unregistered.
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