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 and getCount to have a working adapter.
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 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 |
FragmentPagerAdapter(@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. |
long |
getItemId(int position)Return a unique identifier for the item at the given 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 | |
|---|---|
FragmentPagerAdapter |
public static final int BEHAVIOR_SET_USER_VISIBLE_HINT = 0
Indicates that setUserVisibleHint will be called when the current fragment changes.
| See also | |
|---|---|
FragmentPagerAdapter |
Public constructors
publicFragmentPagerAdapter(@NonNull FragmentManager fm)
Constructor for FragmentPagerAdapter that sets the fragment manager for the adapter. This is the equivalent of calling FragmentPagerAdapter 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 FragmentPagerAdapter(@NonNull FragmentManager fm, int behavior)
Constructor for FragmentPagerAdapter. If BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT is passed in, then only the current Fragment is in the RESUMED state. 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.
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 | |
|---|---|
int position |
Position within this adapter |
| Returns | |
|---|---|
long |
Unique identifier for the item at 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.