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 |
![]() |
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
|
ge |