to top
Android APIs
public abstract class

PagerAdapter

extends Object
java.lang.Object
   ↳ android.support.v4.view.PagerAdapter
Known Direct Subclasses

Class Overview

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 FragmentPagerAdapter or 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(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 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
int POSITION_NONE
int POSITION_UNCHANGED
Public Constructors

? Examples 		PagerAdapter()
Public Methods

? Examples 		void destroyItem( ViewGroup container, int position, Object object)
Remove a page for the given position.

? Examples 		void destroyItem( View container, int position, Object object)
This method was deprecated in API level . Use destroyItem(ViewGroup, int, Object)

? Examples 		void finishUpdate( View container)
This method was deprecated in API level . Use finishUpdate(ViewGroup)

? Examples 		void finishUpdate( ViewGroup container)
Called when the a change in the shown pages has been completed.

? Examples 		abstract int getCount()
Return the number of views available.

? Examples 		int getItemPosition( Object object)
Called when the host view is attempting to determine if an item's position has changed.

? Examples 		CharSequence getPageTitle(int position)
This method may be called by the ViewPager to obtain a title string to describe the specified page.

? Examples 		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]

? Examples 		Object instantiateItem( ViewGroup container, int position)
Create the page for the given position.

? Examples 		Object instantiateItem( View container, int position)
This method was deprecated in API level . Use instantiateItem(ViewGroup, int)

? Examples 		abstract boolean isViewFromObject( View view, Object object)
Determines whether a page View is associated with a specific key object as returned by instantiateItem(ViewGroup, int).

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

? Examples 		void restoreState( Parcelable state, ClassLoader loader)
Restore any instance state associated with this adapter and its pages that was previously saved by saveState().

? Examples 		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.

? Examples 		void setPrimaryItem( View container, int position, Object object)
This method was deprecated in API level . Use setPrimaryItem(ViewGroup, int, Object)

? Examples 		void setPrimaryItem( ViewGroup container, int position, 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.

? Examples 		void startUpdate( View container)
This method was deprecated in API level . Use startUpdate(ViewGroup)

? Examples 		void startUpdate( ViewGroup container)
Called when a change in the shown pages is going to start being made.
[Expand]
Inherited Methods
From class java.lang.Object

Constants

public static final int POSITION_NONE

Constant Value: -2 (0xfffffffe)

public static final int POSITION_UNCHANGED

Constant Value: -1 (0xffffffff)

Public Constructors

public PagerAdapter ()

Public Methods

public void destroyItem (ViewGroup container, int position, 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(ViewGroup).

Parameters
container The containing View from which the page will be removed.
position The page position to be removed.
object The same object that was returned by instantiateItem(View, int).

public void destroyItem (View container, int position, Object object)

This method was deprecated in API level .
Use destroyItem(ViewGroup, int, 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(View).

Parameters
container The containing View from which the page will be removed.
position The page position to be removed.
object The same object that was returned by instantiateItem(View, int).

public void finishUpdate (View container)

This method was deprecated in API level .
Use finishUpdate(ViewGroup)

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

public void finishUpdate (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
container The containing View which is displaying this adapter's page views.

public abstract int getCount ()

Return the number of views available.

public int getItemPosition (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
object Object representing an item, previously returned by a call to instantiateItem(View, int).
Returns

public 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
position The position of the title requested
Returns
  • A title for the requested page

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
position The position of the page requested
Returns
  • Proportional width for the given page position

public Object instantiateItem (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(ViewGroup).

Parameters
container The containing View in which the page will be shown.
position The page position to be instantiated.
Returns
  • Returns an Object representing the new page. This does not need to be a View, but can be some other container of the page.

public Object instantiateItem (View container, int position)

This method was deprecated in API level .
Use instantiateItem(ViewGroup, 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).

Parameters
container The containing View in which the page will be shown.
position The page position to be instantiated.
Returns
  • Returns an Object representing the new page. This does not need to be a View, but can be some other container of the page.

public abstract boolean isViewFromObject (View view, Object object)

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

Parameters
view Page View to check for association with object
object Object to check for association with view
Returns
  • true if view is associated with the key object object

public void notifyDataSetChanged ()

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

public void restoreState (Parcelable state, ClassLoader loader)

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

Parameters
state State previously saved by a call to saveState()
loader A ClassLoader that should be used to instantiate any restored objects

public 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
  • Saved state for this adapter

public void setPrimaryItem (View container, int position, Object object)

This method was deprecated in API level .
Use setPrimaryItem(ViewGroup, int, 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
container The containing View from which the page will be removed.
position The page position that is now the primary.
object The same object that was returned by instantiateItem(View, int).

public void setPrimaryItem (ViewGroup container, int position, 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
container The containing View from which the page will be removed.
position The page position that is now the primary.
object The same object that was returned by instantiateItem(View, int).

public void startUpdate (View container)

This method was deprecated in API level .
Use startUpdate(ViewGroup)

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

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

public void startUpdate (ViewGroup container)

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

Parameters
container The containing View which is displaying this adapter's page views.
No examples for this method.
Frequently called with: [Clear]
Portions of this page are reproduced from work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License. The original page is available here.