FragmentPagerAdapter
public
abstract
class
FragmentPagerAdapter
extends PagerAdapter
java.lang.Object | ||
↳ | androidx.viewpager.widget.PagerAdapter | |
↳ | androidx.fragment.app.FragmentPagerAdapter |
Implementation of PagerAdapter
that
represents each page as a Fragment
that is persistently
kept in the fragment manager as long as the user can return to the page.
This version of the pager is best for use when there are a handful of
typically more static fragments to be paged through, such as a set of tabs.
The fragment of each page the user visits will be kept in memory, though its
view hierarchy may be destroyed when not visible. This can result in using
a significant amount of memory since fragment instances can hold on to an
arbitrary amount of state. For larger sets of pages, consider
FragmentStatePagerAdapter
.
When using FragmentPagerAdapter the host ViewPager must have a valid ID set.
Subclasses only need to implement getItem(int)
and PagerAdapter.getCount()
to have a working adapter.
Here is an example implementation of a pager containing fragments of lists:
public class FragmentPagerSupport extends FragmentActivity { static final int NUM_ITEMS = 10; MyAdapter mAdapter; ViewPager mPager; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.fragment_pager); mAdapter = new MyAdapter(getSupportFragmentManager()); mPager = (ViewPager)findViewById(R.id.pager); mPager.setAdapter(mAdapter); // Watch for button clicks. Button button = (Button)findViewById(R.id.goto_first); button.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { mPager.setCurrentItem(0); } }); button = (Button)findViewById(R.id.goto_last); button.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { mPager.setCurrentItem(NUM_ITEMS-1); } }); } public static class MyAdapter extends FragmentPagerAdapter { public MyAdapter(FragmentManager fm) { super(fm, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT); } @Override public int getCount() { return NUM_ITEMS; } @Override public Fragment getItem(int position) { return ArrayListFragment.newInstance(position); } } public static class ArrayListFragment extends ListFragment { int mNum; /** * Create a new instance of CountingFragment, providing "num" * as an argument. */ static ArrayListFragment newInstance(int num) { ArrayListFragment f = new ArrayListFragment(); // Supply num input as an argument. Bundle args = new Bundle(); args.putInt("num", num); f.setArguments(args); return f; } /** * When creating, retrieve this instance's number from its arguments. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mNum = getArguments() != null ? getArguments().getInt("num") : 1; } /** * The Fragment's UI is just a simple text view showing its * instance number. */ @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View v = inflater.inflate(R.layout.fragment_pager_list, container, false); View tv = v.findViewById(R.id.text); ((TextView)tv).setText("Fragment #" + mNum); return v; } @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); setListAdapter(new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, Cheeses.sCheeseStrings)); } @Override public void onListItemClick(ListView l, View v, int position, long id) { Log.i("FragmentList", "Item clicked: " + id); } } }
The R.layout.fragment_pager
resource of the top-level fragment is:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:padding="4dip" android:gravity="center_horizontal" android:layout_width="match_parent" android:layout_height="match_parent"> <androidx.viewpager.widget.ViewPager android:id="@+id/pager" android:layout_width="match_parent" android:layout_height="0px" android:layout_weight="1"> </androidx.viewpager.widget.ViewPager> <LinearLayout android:orientation="horizontal" android:gravity="center" android:measureWithLargestChild="true" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_weight="0"> <Button android:id="@+id/goto_first" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/first"> </Button> <Button android:id="@+id/goto_last" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/last"> </Button> </LinearLayout> </LinearLayout>
The R.layout.fragment_pager_list
resource containing each
individual fragment's layout is:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@android:drawable/gallery_thumb"> <TextView android:id="@+id/text" android:layout_width="match_parent" android:layout_height="wrap_content" android:gravity="center_vertical|center_horizontal" android:textAppearance="?android:attr/textAppearanceMedium" android:text="@string/hello_world"/> <!-- The frame layout is here since we will be showing either the empty view or the list view. --> <FrameLayout android:layout_width="match_parent" android:layout_height="0dip" android:layout_weight="1" > <!-- Here is the list. Since we are using a ListActivity, we have to call it "@android:id/list" so ListActivity will find it --> <ListView android:id="@android:id/list" android:layout_width="match_parent" android:layout_height="match_parent" android:drawSelectorOnTop="false"/> <!-- Here is the view to show if the list is emtpy --> <TextView android:id="@android:id/empty" android:layout_width="match_parent" android:layout_height="match_parent" android:textAppearance="?android:attr/textAppearanceMedium" android:text="No items."/> </FrameLayout> </LinearLayout>
Summary
Constants | |
---|---|
int |
BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT
Indicates that only the current fragment will be in the |
int |
BEHAVIOR_SET_USER_VISIBLE_HINT
This constant is deprecated.
This behavior relies on the deprecated
|
Inherited constants |
---|
Public constructors | |
---|---|
FragmentPagerAdapter(FragmentManager fm)
This constructor is deprecated.
use |
|
FragmentPagerAdapter(FragmentManager fm, int behavior)
Constructor for |
Public methods | |
---|---|
void
|
destroyItem(ViewGroup container, int position, Object object)
Remove a page for the given position. |
void
|
finishUpdate(ViewGroup container)
Called when the a change in the shown pages has been completed. |
abstract
Fragment
|
getItem(int position)
Return the Fragment associated with a specified position. |
long
|
getItemId(int position)
Return a unique identifier for the item at the given position. |
Object
|
instantiateItem(ViewGroup container, int position)
Create the page for the given position. |
boolean
|
isViewFromObject(View view, Object object)
Determines whether a page View is associated with a specific key object
as returned by |
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
|
startUpdate(ViewGroup container)
Called when a change in the shown pages is going to start being made. |
Inherited methods | |
---|---|
Constants
BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT
public static final int BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT
Indicates that only the current fragment will be in the Lifecycle.State.RESUMED
state. All other Fragments are capped at Lifecycle.State.STARTED
.
Constant Value: 1 (0x00000001)
BEHAVIOR_SET_USER_VISIBLE_HINT
public static final int BEHAVIOR_SET_USER_VISIBLE_HINT
This constant is deprecated.
This behavior relies on the deprecated
Fragment.setUserVisibleHint(boolean)
API. Use
BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT
to switch to its replacement,
FragmentTransaction.setMaxLifecycle(Fragment, Lifecycle.State)
.
Indicates that Fragment.setUserVisibleHint(boolean)
will be called when the current
fragment changes.
Constant Value: 0 (0x00000000)
Public constructors
FragmentPagerAdapter
public FragmentPagerAdapter (FragmentManager fm)
This constructor is deprecated.
use FragmentPagerAdapter(FragmentManager, int)
with
BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT
Constructor for FragmentPagerAdapter
that sets the fragment manager for the adapter.
This is the equivalent of calling FragmentPagerAdapter(FragmentManager, int)
and
passing in BEHAVIOR_SET_USER_VISIBLE_HINT
.
Fragments will have Fragment.setUserVisibleHint(boolean)
called whenever the
current Fragment changes.
Parameters | |
---|---|
fm |
FragmentManager : fragment manager that will interact with this adapter |
FragmentPagerAdapter
public FragmentPagerAdapter (FragmentManager fm, int behavior)
Constructor for FragmentPagerAdapter
.
If BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT
is passed in, then only the current
Fragment is in the Lifecycle.State.RESUMED
state. All other fragments are capped at
Lifecycle.State.STARTED
. If BEHAVIOR_SET_USER_VISIBLE_HINT
is passed, all
fragments are in the Lifecycle.State.RESUMED
state and there will be callbacks to
Fragment.setUserVisibleHint(boolean)
.
Parameters | |
---|---|
fm |
FragmentManager : fragment manager that will interact with this adapter |
behavior |
int : determines if only current fragments are in a resumed state
|
Public methods
destroyItem
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 |
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
PagerAdapter.instantiateItem(View, int) .
|
finishUpdate
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 |
ViewGroup : The containing View which is displaying this adapter's
page views.
|
getItem
public abstract Fragment getItem (int position)
Return the Fragment associated with a specified position.
Parameters | |
---|---|
position |
int |
Returns | |
---|---|
Fragment |
getItemId
public long getItemId (int position)
Return a unique identifier for the item at the given position.
The default implementation returns the given position. Subclasses should override this method if the positions of items can change.
Parameters | |
---|---|
position |
int : Position within this adapter |
Returns | |
---|---|
long |
Unique identifier for the item at position |
instantiateItem
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 |
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. |
isViewFromObject
public 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
|
restoreState
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 |
Parcelable : State previously saved by a call to saveState() |
loader |
ClassLoader : A ClassLoader that should be used to instantiate any restored objects
|
saveState
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 | |
---|---|
Parcelable |
Saved state for this adapter |
setPrimaryItem
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. This method will not be invoked when the adapter contains no items.
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
PagerAdapter.instantiateItem(View, int) .
|
startUpdate
public 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.
|