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 and getCount to have a working adapter.
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 onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, 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_pagerresource 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_listresource 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 empty -->
<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 |
|
|---|---|
static final int |
Indicates that only the current fragment will be in the |
static final int |
This field is deprecated. This behavior relies on the deprecated |
Public constructors |
|---|
|
This method is deprecated. use |
FragmentStatePagerAdapter(@NonNull FragmentManager fm, int behavior)Constructor for |
Public methods |
|
|---|---|
void |
destroyItem(Remove a page for the given position. |
void |
finishUpdate(@NonNull ViewGroup container)Called when the a change in the shown pages has been completed. |
abstract @NonNull Fragment |
getItem(int position)Return the Fragment associated with a specified position. |
@NonNull Object |
instantiateItem(@NonNull ViewGroup container, int position)Create the page for the given position. |
boolean |
isViewFromObject(@NonNull View view, @NonNull Object object)Determines whether a page View is associated with a specific key object as returned by |
void |
restoreState(@Nullable Parcelable state, @Nullable ClassLoader loader)Restore any instance state associated with this adapter and its pages that was previously saved by |
@Nullable Parcelable |
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(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(@NonNull ViewGroup container)Called when a change in the shown pages is going to start being made. |
Inherited Constants |
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Inherited methods |
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Constants
public static final int BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT = 1
Indicates that only the current fragment will be in the RESUMED state. All other Fragments are capped at STARTED.
| See also | |
|---|---|
FragmentStatePagerAdapter |
public static final int BEHAVIOR_SET_USER_VISIBLE_HINT = 0
Indicates that setUserVisibleHint will be called when the current fragment changes.
| See also | |
|---|---|
FragmentStatePagerAdapter |
Public constructors
publicFragmentStatePagerAdapter(@NonNull FragmentManager fm)
Constructor for FragmentStatePagerAdapter that sets the fragment manager for the adapter. This is the equivalent of calling FragmentStatePagerAdapter and passing in BEHAVIOR_SET_USER_VISIBLE_HINT.
Fragments will have setUserVisibleHint called whenever the current Fragment changes.
| Parameters | |
|---|---|
@NonNull FragmentManager fm |
fragment manager that will interact with this adapter |
public FragmentStatePagerAdapter(@NonNull FragmentManager fm, int behavior)
Constructor for FragmentStatePagerAdapter. If BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT is passed in, then only the current Fragment is in the RESUMED state, while all other fragments are capped at STARTED. If BEHAVIOR_SET_USER_VISIBLE_HINT is passed, all fragments are in the RESUMED state and there will be callbacks to setUserVisibleHint.
| Parameters | |
|---|---|
@NonNull FragmentManager fm |
fragment manager that will interact with this adapter |
int behavior |
determines if only current fragments are in a resumed state |
Public methods
destroyItem
public void destroyItem(
@NonNull ViewGroup container,
int position,
@NonNull 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.
| Parameters | |
|---|---|
@NonNull ViewGroup container |
The containing View from which the page will be removed. |
int position |
The page position to be removed. |
@NonNull Object object |
The same object that was returned by |
finishUpdate
public void finishUpdate(@NonNull 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.
public abstract @NonNull Fragment getItem(int position)
Return the Fragment associated with a specified position.
instantiateItem
public @NonNull Object instantiateItem(@NonNull 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.
public boolean isViewFromObject(@NonNull View view, @NonNull Object object)
Determines whether a page View is associated with a specific key object as returned by instantiateItem. This method is required for a PagerAdapter to function properly.
| Parameters | |
|---|---|
@NonNull View view |
Page View to check for association with |
@NonNull Object object |
Object to check for association with |
| Returns | |
|---|---|
boolean |
true if |
restoreState
public void restoreState(@Nullable Parcelable state, @Nullable ClassLoader loader)
Restore any instance state associated with this adapter and its pages that was previously saved by saveState.
| Parameters | |
|---|---|
@Nullable Parcelable state |
State previously saved by a call to |
@Nullable ClassLoader loader |
A ClassLoader that should be used to instantiate any restored objects |
saveState
public @Nullable 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 | |
|---|---|
@Nullable Parcelable |
Saved state for this adapter |
setPrimaryItem
public void setPrimaryItem(
@NonNull ViewGroup container,
int position,
@NonNull 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 | |
|---|---|
@NonNull ViewGroup container |
The containing View from which the page will be removed. |
int position |
The page position that is now the primary. |
@NonNull Object object |
The same object that was returned by |
startUpdate
public void startUpdate(@NonNull ViewGroup container)
Called when a change in the shown pages is going to start being made.