belongs to Maven artifact com.android.support:viewpager:28.0.0-alpha1
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:
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).
Summary
Constants | |
|---|---|
int |
POSITION_NONE
|
int |
POSITION_UNCHANGED
|
Public constructors | |
|---|---|
PagerAdapter()
|
|
Public methods | |
|---|---|
void
|
destroyItem(View container, int position, Object object)
This method was deprecated
in API level 22.1.0.
Use |
void
|
destroyItem(ViewGroup container, int position, Object object)
Remove a page for the given position. |
void
|
finishUpdate(View container)
This method was deprecated
in API level 22.1.0.
Use |
void
|
finishUpdate(ViewGroup container)
Called when 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 was deprecated
in API level 22.1.0.
Use |
abstract
boolean
|
isViewFromObject(View view, Object object)
Determines whether a page View is associated with a specific key object
as returned by |
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 |
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(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(View container, int position, Object object)
This method was deprecated
in API level 22.1.0.
Use |
void
|
startUpdate(ViewGroup container)
Called when a change in the shown pages is going to start being made. |
void
|
startUpdate(View container)
This method was deprecated
in API level 22.1.0.
Use |
void
|
unregisterDataSetObserver(DataSetObserver observer)
Unregister an observer from callbacks related to the adapter's data changing. |
Inherited methods | |
|---|---|
From
class
java.lang.Object
| |
Constants
Public constructors
Public methods
destroyItem
void destroyItem (View container, int position, Object object)
This method was deprecated
in API level 22.1.0.
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). |
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).
|
finishUpdate
void finishUpdate (View container)
This method was deprecated
in API level 22.1.0.
Use finishUpdate(ViewGroup)
Called when 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 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.
|
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 | |
|---|---|