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PagerAdapter

public abstract class PagerAdapter
extends Object

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

PagerAdapter()

Public methods

void destroyItem(ViewGroup container, int position, Object object)

Remove a page for the given position.

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

This method is deprecated. Use destroyItem(ViewGroup, int, Object)

void finishUpdate(View container)

This method is deprecated. Use finishUpdate(ViewGroup)

void finishUpdate(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(ViewGroup container, int position)

Create the page for the given position.

Object instantiateItem(View container, int position)

This method is deprecated. Use instantiateItem(ViewGroup, int)

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).

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(DataSetObserver observer)

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

void restoreState(Parcelable state, ClassLoader loader)

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

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(View container, int position, Object object)

This method is deprecated. Use setPrimaryItem(ViewGroup, int, Object)

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.

void startUpdate(View container)

This method is deprecated. Use startUpdate(ViewGroup)

void startUpdate(ViewGroup container)

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

void unregisterDataSetObserver(DataSetObserver observer)

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

Inherited methods

From class java.lang.Object

Constants

POSITION_NONE

int POSITION_NONE

Constant Value: -2 (0xfffffffe)

POSITION_UNCHANGED

int POSITION_UNCHANGED

Constant Value: -1 (0xffffffff)

Public constructors

PagerAdapter

PagerAdapter ()

Public methods

destroyItem

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

destroyItem

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

This method is 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 View: The containing View from which the page will be removed.
position int: The page position to be removed.
object Object: The same object that was returned by instantiateItem(View, int).

finishUpdate

void finishUpdate (View container)

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

finishUpdate

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

getCount

int getCount ()

Return the number of views available.

Returns
int

getItemPosition

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: Object representing an item, previously returned by a call to instantiateItem(View, int).
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

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 int: The position of the title requested
Returns
CharSequence A title for the requested page

getPageWidth

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 int: The position of the page requested
Returns
float Proportional width for the given page position

instantiateItem

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 ViewGroup: The containing View in which the page will be shown.
position int: The page position to be instantiated.
Returns
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

Object instantiateItem (View container, 
                int position)

This method is 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 View: The containing View in which the page will be shown.
position int: The page position to be instantiated.
Returns
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

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

notifyDataSetChanged

void notifyDataSetChanged ()

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

registerDataSetObserver

void registerDataSetObserver (DataSetObserver observer)

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

Parameters
observer DataSetObserver: The DataSetObserver which will receive callbacks.

restoreState

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

saveState

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
Parcelable Saved state for this adapter

setPrimaryItem

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

This method is 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 View: The containing View from which the page will be removed.
position int: The page position that is now the primary.
object Object: The same object that was returned by instantiateItem(View, int).

setPrimaryItem

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

startUpdate

void startUpdate (View container)

This method is deprecated.
Use startUpdate(ViewGroup)

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

void startUpdate (ViewGroup container)

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

void unregisterDataSetObserver (DataSetObserver observer)

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

Parameters
observer DataSetObserver: The DataSetObserver which will be unregistered.
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