android.support.v4.view
Class PagerAdapter

java.lang.Object
  android.support.v4.view.PagerAdapter

Direct Known Subclasses:

FragmentPagerAdapter, FragmentStatePagerAdapter

public abstract class PagerAdapter
extends Object

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:

• 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 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).

Field Summary

static int	POSITION_NONE
static int	POSITION_UNCHANGED

Constructor Summary

PagerAdapter()

Method Summary

void	destroyItem(android.view.ViewGroup container, int position, Object object) Remove a page for the given position.
void	destroyItem(android.view.View container, int position, Object object) Deprecated. Use destroyItem(ViewGroup, int, Object)
void	finishUpdate(android.view.View container) Deprecated. Use finishUpdate(ViewGroup)
void	finishUpdate(android.view.ViewGroup container) Called when the a change in the shown pages has been completed.
abstract int	getCount() Return the number of views available.
int	getItemPosition(Object object) Called when the host view is attempting to determine if an item's position has changed.
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]
Object	instantiateItem(android.view.ViewGroup container, int position) Create the page for the given position.
Object	instantiateItem(android.view.View container, int position) Deprecated. Use instantiateItem(ViewGroup, int)
abstract boolean	isViewFromObject(android.view.View view, Object object) Determines whether a page View is associated with a specific key object as returned by instantiateItem(ViewGroup, int).
void	notifyDataSetChanged() This method should be called by the application if the data backing this adapter has changed and associated views should update.
void	registerDataSetObserver(android.database.DataSetObserver observer) Register an observer to receive callbacks related to the adapter's data changing.
void	restoreState(android.os.Parcelable state, ClassLoader loader) Restore any instance state associated with this adapter and its pages that was previously saved by saveState().
android.os.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.
void	setPrimaryItem(android.view.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.
void	setPrimaryItem(android.view.View container, int position, Object object) Deprecated. Use setPrimaryItem(ViewGroup, int, Object)
void	startUpdate(android.view.View container) Deprecated. Use startUpdate(ViewGroup)
void	startUpdate(android.view.ViewGroup container) Called when a change in the shown pages is going to start being made.
void	unregisterDataSetObserver(android.database.DataSetObserver observer) Unregister an observer from callbacks related to the adapter's data changing.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

POSITION_UNCHANGED

public static final int POSITION_UNCHANGED

See Also:

Constant Field Values

POSITION_NONE

public static final int POSITION_NONE

See Also:

Constant Field Values

Constructor Detail

PagerAdapter

public PagerAdapter()

Method Detail

getCount

public abstract int getCount()

Return the number of views available.

startUpdate

public void startUpdate(android.view.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.

instantiateItem

public Object instantiateItem(android.view.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.

destroyItem

public void destroyItem(android.view.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).

setPrimaryItem

public void setPrimaryItem(android.view.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).

finishUpdate

public void finishUpdate(android.view.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.

startUpdate

public void startUpdate(android.view.View container)

Deprecated. 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.

instantiateItem

public Object instantiateItem(android.view.View container,
                              int position)

Deprecated. 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.

destroyItem

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

Deprecated. 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).

setPrimaryItem

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

Deprecated. 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).

finishUpdate

public void finishUpdate(android.view.View container)

Deprecated. 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.

isViewFromObject

public abstract boolean isViewFromObject(android.view.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

saveState

public android.os.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

restoreState

public void restoreState(android.os.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

getItemPosition

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:

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.

notifyDataSetChanged

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

public void registerDataSetObserver(android.database.DataSetObserver observer)

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

Parameters:

observer - The DataSetObserver which will receive callbacks.

unregisterDataSetObserver

public void unregisterDataSetObserver(android.database.DataSetObserver observer)

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

Parameters:

observer - The DataSetObserver which will be unregistered.

getPageTitle

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

getPageWidth

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