FragmentStatePagerAdapter

public abstract class FragmentStatePagerAdapter
extends PagerAdapter

java.lang.Object
   ↳ androidx.viewpager.widget.PagerAdapter
     ↳ androidx.fragment.app.FragmentStatePagerAdapter

Implementation of PagerAdapter that uses a Fragment to manage each page. This class also handles saving and restoring of fragment's state.

This version of the pager is more useful when there are a large number of pages, working more like a list view. When pages are not visible to the user, their entire fragment may be destroyed, only keeping the saved state of that fragment. This allows the pager to hold on to much less memory associated with each visited page as compared to FragmentPagerAdapter at the cost of potentially more overhead when switching between pages.

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 FragmentStatePagerSupport 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 FragmentStatePagerAdapter {
        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 Lifecycle.State.RESUMED state.

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).

Inherited constants

Public constructors

FragmentStatePagerAdapter(FragmentManager fm)

This constructor is deprecated. use FragmentStatePagerAdapter(FragmentManager, int) with BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT

FragmentStatePagerAdapter(FragmentManager fm, int behavior)

Constructor for FragmentStatePagerAdapter.

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.

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 instantiateItem(ViewGroup, int).

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(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

FragmentStatePagerAdapter

public FragmentStatePagerAdapter (FragmentManager fm)

This constructor is deprecated.
use FragmentStatePagerAdapter(FragmentManager, int) with BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT

Constructor for FragmentStatePagerAdapter that sets the fragment manager for the adapter. This is the equivalent of calling FragmentStatePagerAdapter(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

FragmentStatePagerAdapter

public FragmentStatePagerAdapter (FragmentManager fm, 
                int behavior)

Constructor for FragmentStatePagerAdapter. If BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT is passed in, then only the current Fragment is in the Lifecycle.State.RESUMED state, while 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

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.