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Tab+ViewPager not updating instead shows weird warning expected state 3 found 2

I have a mainactivity which includes a TabLayout with ViewPager
I have added 3 tabs and each tab has separate fragments which contains a recyclerview, and these recyclerviews has a checkbox that should be simultaneously updated/refreshed whenever i swipe the viewpager(i save checked positions in shared preference and updates via shared preference).
My problem here is whenever i check a checkbox in tab1, tab2 is not updating/refreshing until i scroll down the Recyclerview. and tab3 is working fine.
and i am getting a weird warning in logcat too.
03-05 09:35:53.345 4317-4327/com.example.rubin W/art: Suspending all threads took: 6.805ms
03-05 09:35:58.310 4317-4317/com.example.rubin W/FragmentManager: moveToState: Fragment state for Tab3{10a5f1f0 #2 id=0x7f0d00b6} not updated inline; expected state 3 found 2
03-05 09:36:01.363 4317-4317/com.example.rubin W/FragmentManager: moveToState: Fragment state for Tab1{2d9aa887 #1 id=0x7f0d00b6} not updated inline; expected state 3 found 2
My PagerAdapter
public class PagerAdapter1 extends FragmentStatePagerAdapter {
int mNumOfTabs;
public PagerAdapter1(FragmentManager fm, int NumOfTabs) {
super(fm);
this.mNumOfTabs = NumOfTabs;
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new Tab1();
case 1:
return new Tab2();
case 2:
return new Tab3();
default:
return null;
}
}
#Override
public int getCount() {
return mNumOfTabs;
}
}
Tablayout OnPageChangelistener
final PagerAdapter1 adapter = new PagerAdapter1
(getSupportFragmentManager(), tabLayout1.getTabCount(), getApplicationContext());
viewPager1.setAdapter(adapter);
viewPager1.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout1));
tabLayout1.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
#Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager1.setCurrentItem(tab.getPosition());
adapter.notifyDataSetChanged();
}
#Override
public void onTabUnselected(TabLayout.Tab tab) {
}
#Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
code for each fragments.
public class Tab1 extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.home_tab1_recycler, container, false);
RecyclerView rv = (RecyclerView) v.findViewById(R.id.home_recyclerview);
LinearLayoutManager llm = new LinearLayoutManager(getContext());
rv.setLayoutManager(llm);
rv.setHasFixedSize(true); // to improve performance
rv.setAdapter(new HomeManager()); // the projectdatabase manager is assigner to the RV
return v;
}
public class HomeManager extends RecyclerView.Adapter<HomeManager.RecyclerViewHolder> {
int Length,h;
View v1;
ArrayList<String> PROJECT_ID = new ArrayList<String>();
Set<String> set;
List<String> selected;
public class RecyclerViewHolder extends RecyclerView.ViewHolder {
CheckBox mCheck;
RecyclerViewHolder(final View itemView) {
super(itemView);
mCheck = (CheckBox) itemView.findViewById(R.id.PROJECT_fav);
SharedPreferences pref = getContext().getSharedPreferences("MirSP", Context.MODE_PRIVATE);
set = pref.getStringSet("FAV", null);
if (set != null) {
selected = new ArrayList<String>(set);
} else {
selected = new ArrayList<String>();
}
mCheck.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
h = getAdapterPosition();
check = PROJECT_ID.get(h); // for saving the project id from json.
if (selected.contains(check)) {
selected.remove(check);
mCheck.setBackgroundResource(R.drawable.ic_favorite_white1_24dp);
Snackbar snackbar = Snackbar.make(v, "Property Unfavorited", Snackbar.LENGTH_SHORT);
snackbar.show();
} else {
selected.add(check);
mCheck.setBackgroundResource(R.drawable.ic_favorite_white_24dp);
Snackbar snackbar = Snackbar.make(v, "Property Favorited", Snackbar.LENGTH_SHORT);
snackbar.show();
}
Log.e("HF update checked", String.valueOf(selected));
Set<String> set = new HashSet<String>();
set.addAll(selected);
SharedPreferences pref = getContext().getSharedPreferences("MirSP", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = pref.edit();
editor.putStringSet("FAV", set);
editor.commit();
}
}
});
#Override
public RecyclerViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
v1 = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.recyclerview_item, viewGroup, false);
return new RecyclerViewHolder(v1);
}
#Override
public void onBindViewHolder(final RecyclerViewHolder viewHolder, int i) {
SharedPreferences pref = getContext().getSharedPreferences("MirSP", Context.MODE_PRIVATE);
set = pref.getStringSet("FAV", null);
if (set != null) {
selected = new ArrayList<String>(set);
} else {
selected = new ArrayList<String>();
}
Log.e("HF update UI", String.valueOf(selected));
if (String.valueOf(selected).contains(String.valueOf(PROJECT_ID.get(i)))) {
viewHolder.mCheck.setBackgroundResource(R.drawable.ic_favorite_white_24dp);
} else {
viewHolder.mCheck.setBackgroundResource(R.drawable.ic_favorite_white1_24dp);
}
}
#Override
public int getItemCount() {
//Code for Total length of json
return Length;
}

The FragmentPagerAdapter calls setUserVisibleHint(true|false) on neighbourhoods of the active fragment which changes the state of this fragments.
This is at least the answer of the "weird warning messages" but it may not solve your problem.
Regarding your comment about how to solve that warning message I have created my own FragmentPagerAdapter as follows:
public abstract class AbstractTabPagerAdapter extends PagerAdapter {
private static final String TAG = AbstractTabPagerAdapter.class.getCanonicalName();
private final FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction;
private Fragment mCurrentPrimaryItem = null;
public AbstractTabPagerAdapter(FragmentManager fragmentManager) {
mFragmentManager = fragmentManager;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
throw new IllegalArgumentException("current transaction must not be null");
}
String fragmentTag = makeFragmentName(container.getId(), position);
Fragment fragment = (Fragment) mFragmentManager.findFragmentByTag(fragmentTag);
if (fragment != null) {
mCurTransaction.attach(fragment);
Log.d(TAG, "Attaching existing fragment " + fragment + " at position " + position);
//mCurTransaction.add(container.getId(), fragment, makeFragmentName(container.getId(), position));
} else {
fragment = getItem(position);
mCurTransaction.add(container.getId(), fragment, fragmentTag);
Log.d(TAG, "Attaching new fragment " + fragment + " at position " + position);
}
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
//fragment.setUserVisibleHint(false);
}
return fragment;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
if (mCurTransaction == null) {
throw new IllegalArgumentException("current transaction must not be null");
}
mCurTransaction.detach((Fragment) object);
//mCurTransaction.remove((Fragment)object);
}
#Override
public void setPrimaryItem(ViewGroup container, int position, Object object) {
//super.setPrimaryItem(container, position, object);
Fragment fragment = (Fragment) object;
if (fragment != mCurrentPrimaryItem) {
Log.d(TAG, "set Primary item " + position + " to " + fragment);
if (mCurrentPrimaryItem != null) {
mCurrentPrimaryItem.setMenuVisibility(false);
// this command unexpectedly changes the state of the fragment which leads to a warning message and possible some strange behaviour
//mCurrentPrimaryItem.setUserVisibleHint(false);
}
if (fragment != null) {
fragment.setMenuVisibility(true);
//fragment.setUserVisibleHint(true);
}
mCurrentPrimaryItem = fragment;
}
}
#Override
public boolean isViewFromObject(View view, Object fragment) {
return ((Fragment) fragment).getView() == view;
}
public abstract Fragment getItem(int position);
#Override
public void startUpdate(ViewGroup container) {
super.startUpdate(container);
if (mCurTransaction != null) {
throw new IllegalArgumentException("current transaction must not be null");
}
mCurTransaction = mFragmentManager.beginTransaction();
Log.d(TAG, "FragmentTransaction started");
}
#Override
public void finishUpdate(ViewGroup container) {
if (mCurTransaction != null) {
mCurTransaction.commit();
mCurTransaction = null;
//mFragmentManager.executePendingTransactions();
Log.d(TAG, "FragmentTransaction committed");
} else {
throw new IllegalArgumentException("current transaction must not be null");
}
}
private String makeFragmentName(int viewId, int position) {
if (viewId <= 0)
throw new IllegalArgumentException("viewId " + viewId);
return "tabpageradptr:" + getPageTitle(position) + ":" + viewId + ":" + position;
}
}
The warning message is gone now and currently I do not experience any flaws - but I am still in the middle of research.

I spent a lot of time for this issue. Problem is you try to update viewpager in OnPageChangeListener listener, it will throw warning
not update in line
Solution:
All data change and update view should call out of OnPageChangeListener,
ex: onCreateView of Fragment
My warning was gone! And viewpager update completelly

Its late but i figured a best way out using FragmentPagerAdapter , though its not eliminating the warnings, but its solving the purpose, if anyone can inform me what does that warning actually means and whats actually causing the warning, it would be of my best interest.
First in all of the fragments used in the viewpager create method as below.
public void updateView() {
//Update whatever views or data you want to update
}
Also override method setUserVisibleHint which is used in FragmentPagerAdapter to notify if the fragment is visible to user or not.
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
this.isVisibleToUser = isVisibleToUser;
super.setUserVisibleHint(isVisibleToUser);
}
finally in your fragment add the following code to update the view/date when the fragment is visible.
#Override
public void onStart() {
if (isVisibleToUser)
updateView();
}
Then implement this in your TabFragment or Activity
viewpager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
switch (position) {
case 0: {
((Fragment) mFragmentList.get(0)).updateView();
break;
}
case 1: {
((Fragment) mFragmentList.get(1)).updateView();
break;
}
}
}
This will take care of update the data consistantly, either you swipe or you click the tab, if anyone finds any issues or bugs, please comment and let me know or feel free to edit the solution
And I have voted for the solution above which gave me approach to apply this solution. Thanks #mikes

It is not a important. It is only a warning.
Please try to change the background of ViewPager layout to null(not set the background).

In view pager adjacent tabs are loaded simultaneously. So your actions in tab 1 will not be reflected in tab 2 since its already loaded. You should be using Broadcast receivers to solve this issue. Broadcast a event in tab 1 and receive the event in tab 2

The "W/FragmentManager: moveToState: … expected state 3 found 2" warning can be ignored and was removed in Support Library v24.0.0.
Quote from the official developer answer:
You don't need to do anything additional; this is an informational log message only.
[…]
The log itself as described here does not affect behavior. Please open
a new bug if you are having other issues; conflating different issues
in the same bug makes those separate issues more difficult to track.
Closing comments as the log issue has been resolved for a future
release.

Set data in Fragments from ViewPager [duplicate]

I'm using the v4 compatibility ViewPager in Android. My FragmentActivity has a bunch of data which is to be displayed in different ways on different pages in my ViewPager. So far I just have 3 instances of the same ListFragment, but in the future I will have 3 instances of different ListFragments. The ViewPager is on a vertical phone screen, the lists are not side-by-side.
Now a button on the ListFragment starts an separate full-page activity (via the FragmentActivity), which returns and FragmentActivity modifies the data, saves it, then attempts to update all views in its ViewPager. It is here, where I am stuck.
public class ProgressMainActivity extends FragmentActivity
{
MyAdapter mAdapter;
ViewPager mPager;
#Override
public void onCreate(Bundle savedInstanceState)
{
...
mAdapter = new MyAdapter(getSupportFragmentManager());
mPager = (ViewPager) findViewById(R.id.viewpager);
mPager.setAdapter(mAdapter);
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{
...
updateFragments();
...
}
public void updateFragments()
{
//Attempt 1:
//mAdapter.notifyDataSetChanged();
//mPager.setAdapter(mAdapter);
//Attempt 2:
//HomeListFragment fragment = (HomeListFragment) getSupportFragmentManager().findFragmentById(mAdapter.fragId[0]);
//fragment.updateDisplay();
}
public static class MyAdapter extends FragmentPagerAdapter implements
TitleProvider
{
int[] fragId = {0,0,0,0,0};
public MyAdapter(FragmentManager fm)
{
super(fm);
}
#Override
public String getTitle(int position){
return titles[position];
}
#Override
public int getCount(){
return titles.length;
}
#Override
public Fragment getItem(int position)
{
Fragment frag = HomeListFragment.newInstance(position);
//Attempt 2:
//fragId[position] = frag.getId();
return frag;
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE; //To make notifyDataSetChanged() do something
}
}
public class HomeListFragment extends ListFragment
{
...
public static HomeListFragment newInstance(int num)
{
HomeListFragment f = new HomeListFragment();
...
return f;
}
...
Now as you can see, my first attempt was to notifyDataSetChanged on the entire FragmentPagerAdapter, and this showed to update the data sometimes, but others I got an IllegalStateException: Can not perform this action after onSaveInstanceState.
My second attempt involed trying to call an update function in my ListFragment, but getId in getItem returned 0. As per the docs I tried by
acquiring a reference to the Fragment from FragmentManager, using
findFragmentById() or findFragmentByTag()
but I don't know the tag or id of my Fragments! I have an android:id="#+id/viewpager" for ViewPager, and a android:id="#android:id/list" for my ListView in the ListFragment layout, but I don't think these are useful.
So, how can I either:
a) update the entire ViewPager safely in one go (ideally returning the user to the page he was on before) - it is ok that the user see the view change.
Or preferably,
b) call a function in each affected ListFragment to update the ListView manually.
Any help would be gratefully accepted!

Barkside's answer works with FragmentPagerAdapter but doesn't work with FragmentStatePagerAdapter, because it doesn't set tags on fragments it passes to FragmentManager.
With FragmentStatePagerAdapter it seems we can get by, using its instantiateItem(ViewGroup container, int position) call. It returns reference to fragment at position position. If FragmentStatePagerAdapter already holds reference to fragment in question, instantiateItem just returns reference to that fragment, and doesn't call getItem() to instantiate it again.
So, suppose, I'm currently looking at fragment #50, and want to access fragment #49. Since they are close, there's a good chance the #49 will be already instantiated. So,
ViewPager pager = findViewById(R.id.viewpager);
FragmentStatePagerAdapter a = (FragmentStatePagerAdapter) pager.getAdapter();
MyFragment f49 = (MyFragment) a.instantiateItem(pager, 49)

OK, I think I've found a way to perform request b) in my own question so I'll share for others' benefit. The tag of fragments inside a ViewPager is in the form "android:switcher:VIEWPAGER_ID:INDEX", where VIEWPAGER_ID is the R.id.viewpager in XML layout, and INDEX is the position in the viewpager. So if the position is known (eg 0), I can perform in updateFragments():
HomeListFragment fragment =
(HomeListFragment) getSupportFragmentManager().findFragmentByTag(
"android:switcher:"+R.id.viewpager+":0");
if(fragment != null) // could be null if not instantiated yet
{
if(fragment.getView() != null)
{
// no need to call if fragment's onDestroyView()
//has since been called.
fragment.updateDisplay(); // do what updates are required
}
}
I've no idea if this is a valid way of doing it, but it'll do until something better is suggested.

Try to record the tag each time a Fragement is instantiated.
public class MPagerAdapter extends FragmentPagerAdapter {
private Map<Integer, String> mFragmentTags;
private FragmentManager mFragmentManager;
public MPagerAdapter(FragmentManager fm) {
super(fm);
mFragmentManager = fm;
mFragmentTags = new HashMap<Integer, String>();
}
#Override
public int getCount() {
return 10;
}
#Override
public Fragment getItem(int position) {
return Fragment.instantiate(mContext, AFragment.class.getName(), null);
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Object obj = super.instantiateItem(container, position);
if (obj instanceof Fragment) {
// record the fragment tag here.
Fragment f = (Fragment) obj;
String tag = f.getTag();
mFragmentTags.put(position, tag);
}
return obj;
}
public Fragment getFragment(int position) {
String tag = mFragmentTags.get(position);
if (tag == null)
return null;
return mFragmentManager.findFragmentByTag(tag);
}
}

If you ask me, the second solution on the below page, keeping track of all the "active" fragment pages, is better: http://tamsler.blogspot.nl/2011/11/android-viewpager-and-fragments-part-ii.html
The answer from barkside is too hacky for me.
you keep track of all the "active" fragment pages. In this case, you keep track of the fragment pages in the FragmentStatePagerAdapter, which is used by the ViewPager.
private final SparseArray<Fragment> mPageReferences = new SparseArray<Fragment>();
public Fragment getItem(int index) {
Fragment myFragment = MyFragment.newInstance();
mPageReferences.put(index, myFragment);
return myFragment;
}
To avoid keeping a reference to "inactive" fragment pages, we need to implement the FragmentStatePagerAdapter's destroyItem(...) method:
public void destroyItem(View container, int position, Object object) {
super.destroyItem(container, position, object);
mPageReferences.remove(position);
}
... and when you need to access the currently visible page, you then call:
int index = mViewPager.getCurrentItem();
MyAdapter adapter = ((MyAdapter)mViewPager.getAdapter());
MyFragment fragment = adapter.getFragment(index);
... where the MyAdapter's getFragment(int) method looks like this:
public MyFragment getFragment(int key) {
return mPageReferences.get(key);
}
"

Okay, after testing the method by #barkside above, I could not get it to work with my application. Then I remembered that the IOSched2012 app uses a viewpager as well, and that is where I found my solution. It does not use any fragment ID's or Tags as these are not stored by viewpager in an easily accessible way.
Here's the important parts from the IOSched apps HomeActivity. Pay particular attention to the comment, as therein lies the key.:
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
// Since the pager fragments don't have known tags or IDs, the only way to persist the
// reference is to use putFragment/getFragment. Remember, we're not persisting the exact
// Fragment instance. This mechanism simply gives us a way to persist access to the
// 'current' fragment instance for the given fragment (which changes across orientation
// changes).
//
// The outcome of all this is that the "Refresh" menu button refreshes the stream across
// orientation changes.
if (mSocialStreamFragment != null) {
getSupportFragmentManager().putFragment(outState, "stream_fragment",
mSocialStreamFragment);
}
}
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
if (mSocialStreamFragment == null) {
mSocialStreamFragment = (SocialStreamFragment) getSupportFragmentManager()
.getFragment(savedInstanceState, "stream_fragment");
}
}
And store instances of you Fragments in the FragmentPagerAdapter like so:
private class HomePagerAdapter extends FragmentPagerAdapter {
public HomePagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return (mMyScheduleFragment = new MyScheduleFragment());
case 1:
return (mExploreFragment = new ExploreFragment());
case 2:
return (mSocialStreamFragment = new SocialStreamFragment());
}
return null;
}
Also, remember to guard your Fragment calls like so:
if (mSocialStreamFragment != null) {
mSocialStreamFragment.refresh();
}

You can copy FragmentPagerAdapter and modify some source code, add getTag() method
for example
public abstract class AppFragmentPagerAdapter extends PagerAdapter {
private static final String TAG = "FragmentPagerAdapter";
private static final boolean DEBUG = false;
private final FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction = null;
private Fragment mCurrentPrimaryItem = null;
public AppFragmentPagerAdapter(FragmentManager fm) {
mFragmentManager = fm;
}
public abstract Fragment getItem(int position);
#Override
public void startUpdate(ViewGroup container) {
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
final long itemId = getItemId(position);
String name = getTag(position);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);
} else {
fragment = getItem(position);
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,
getTag(position));
}
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object
+ " v=" + ((Fragment) object).getView());
mCurTransaction.detach((Fragment) object);
}
#Override
public void setPrimaryItem(ViewGroup container, int position, Object object) {
Fragment fragment = (Fragment) object;
if (fragment != mCurrentPrimaryItem) {
if (mCurrentPrimaryItem != null) {
mCurrentPrimaryItem.setMenuVisibility(false);
mCurrentPrimaryItem.setUserVisibleHint(false);
}
if (fragment != null) {
fragment.setMenuVisibility(true);
fragment.setUserVisibleHint(true);
}
mCurrentPrimaryItem = fragment;
}
}
#Override
public void finishUpdate(ViewGroup container) {
if (mCurTransaction != null) {
mCurTransaction.commitAllowingStateLoss();
mCurTransaction = null;
mFragmentManager.executePendingTransactions();
}
}
#Override
public boolean isViewFromObject(View view, Object object) {
return ((Fragment) object).getView() == view;
}
#Override
public Parcelable saveState() {
return null;
}
#Override
public void restoreState(Parcelable state, ClassLoader loader) {
}
public long getItemId(int position) {
return position;
}
private static String makeFragmentName(int viewId, long id) {
return "android:switcher:" + viewId + ":" + id;
}
protected abstract String getTag(int position);
}
then extend it, override these abstract method,don't need to be afraid of Android Group change
FragmentPageAdapter source code in the future
class TimeLinePagerAdapter extends AppFragmentPagerAdapter {
List<Fragment> list = new ArrayList<Fragment>();
public TimeLinePagerAdapter(FragmentManager fm) {
super(fm);
list.add(new FriendsTimeLineFragment());
list.add(new MentionsTimeLineFragment());
list.add(new CommentsTimeLineFragment());
}
public Fragment getItem(int position) {
return list.get(position);
}
#Override
protected String getTag(int position) {
List<String> tagList = new ArrayList<String>();
tagList.add(FriendsTimeLineFragment.class.getName());
tagList.add(MentionsTimeLineFragment.class.getName());
tagList.add(CommentsTimeLineFragment.class.getName());
return tagList.get(position);
}
#Override
public int getCount() {
return list.size();
}
}

Also works without problems:
somewhere in page fragment's layout:
<FrameLayout android:layout_width="0dp" android:layout_height="0dp" android:visibility="gone" android:id="#+id/fragment_reference">
<View android:layout_width="0dp" android:layout_height="0dp" android:visibility="gone"/>
</FrameLayout>
in fragment's onCreateView():
...
View root = inflater.inflate(R.layout.fragment_page, container, false);
ViewGroup ref = (ViewGroup)root.findViewById(R.id.fragment_reference);
ref.setTag(this);
ref.getChildAt(0).setTag("fragment:" + pageIndex);
return root;
and method to return Fragment from ViewPager, if exists:
public Fragment getFragment(int pageIndex) {
View w = mViewPager.findViewWithTag("fragment:" + pageIndex);
if (w == null) return null;
View r = (View) w.getParent();
return (Fragment) r.getTag();
}

Alternatively you can override setPrimaryItem method from FragmentPagerAdapter like so:
public void setPrimaryItem(ViewGroup container, int position, Object object) {
if (mCurrentFragment != object) {
mCurrentFragment = (Fragment) object; //Keep reference to object
((MyInterface)mCurrentFragment).viewDidAppear();//Or call a method on the fragment
}
super.setPrimaryItem(container, position, object);
}
public Fragment getCurrentFragment(){
return mCurrentFragment;
}

I want to give my approach in case it can help anyone else:
This is my pager adapter:
public class CustomPagerAdapter extends FragmentStatePagerAdapter{
private Fragment[] fragments;
public CustomPagerAdapter(FragmentManager fm) {
super(fm);
fragments = new Fragment[]{
new FragmentA(),
new FragmentB()
};
}
#Override
public Fragment getItem(int arg0) {
return fragments[arg0];
}
#Override
public int getCount() {
return fragments.length;
}
}
In my activity I have:
public class MainActivity {
private ViewPager view_pager;
private CustomPagerAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
adapter = new CustomPagerAdapter(getSupportFragmentManager());
view_pager = (ViewPager) findViewById(R.id.pager);
view_pager.setAdapter(adapter);
view_pager.setOnPageChangeListener(this);
...
}
}
Then to get the current fragment what I do is:
int index = view_pager.getCurrentItem();
Fragment currentFragment = adapter.getItem(index);

This is my solution since I don't need to keep track of my tabs and need to refresh them all anyway.
Bundle b = new Bundle();
b.putInt(Constants.SharedPreferenceKeys.NUM_QUERY_DAYS,numQueryDays);
for(android.support.v4.app.Fragment f:getSupportFragmentManager().getFragments()){
if(f instanceof HomeTermFragment){
((HomeTermFragment) f).restartLoader(b);
}
}

Can I use setCurrentItem in viewPager and use onPageSelected?

My problem is to initially load the fragment directly and also I want to call a method fragment is visible to the user.
For loading the correct fragment, I use viewPager.setCurrentItem() in onCreate. It works well.
FragmentActivity code:
public void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
mTabsAdapter = new TabsPlayerAdapter(this, mRadioList);
mMainViewPager.setAdapter(mTabsAdapter);
mMainViewPager.setOnPageChangeListener(this);
mMainViewPager.setCurrentItem(2);
}
To a method called fragment Current, I use the onPageSelected viewPager. It works well.
FragmentActivity code:
#Override
public void onPageSelected(int position) {
Log.d(TAG, "onPageSelected - position: " + position);
((PlayerFragment) mTabsAdapter.mSparseFragment.get(position))
.startAnnimation();
}
FragmentStatePagerAdapter code:
#Override
public Fragment getItem(final int position) {
Log.d(TAG, "getItem - position: " + position);
Bundle args = new Bundle();
args.putString("num", mRadioModel.get(position).name);
mSparseFragment.put(position, Fragment.instantiate
(mContext,PlayerFragment.class.getName(), args));
return mSparseFragment.get(position);
}
FragmentStatePagerAdapter code :
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
super.destroyItem(container, position, object);
Log.d(TAG, "destroyItem - position: " + position);
mSparseFragment.remove(position);
}
I can do these two things separately. But when I try to use the two together, I have a "NullPointerException" when I call my fragment.
I saw that onPageSelected is called before the getItem in my Adapter.

There is very easy work around:
In your adapter write:
public static interface FirstShot
{
public void onFirstShot();
}
private FirstShot firstShot;
private boolean shot = false;
#Override
public Fragment getItem(int arg0)
{
if (!shot && firstShot != null)
{
shot = true;
firstShot.onFirstShot();
}
// your code here
}
Now implement FirstShot in activity:
#Override
public void onFirstShot()
{
viewPager.post(new Runnable()
{
#Override
public void run()
{
boolean needNotify = false;
if (pager.getCurrentItem() == position) needNotify = true;
viewPager.setCurrentItem(position, false);
if (needNotify) onPageSelected(position);
}
});
}
onPageSelected() now calls!

You'll know that items are available when onAttachedToWindow is called. At the moment you call setCurrentItem, the adapter has not been used to create views yet. (setAdapter is not sufficient to know that all have been inflated)
Else, you can consider setting your listener after setting the currentItem, therefore not having a animation when opening the fragment.

The accepted solution didn't work for me, as I was still getting onPageSelected called before getItem created them.
I fixed it like so:
public class MyAdapter extends FragmentPagerAdapter {
...
...
#Override
public Fragment getItem(int position) {
Fragment fragment = createdFragments.get(position);
if (fragment != null) {
return fragment;
}
fragment = createNewFragment();
createdFragments.put(position, fragment);
return fragment;
}
public TabFragment getFragment(int position) {
TabFragment fragment = createdFragments.get(position);
if (fragment == null) {
fragment = (TabFragment) getItem(position);
}
return fragment;
}
}
and then I use adapter.getFragment() to get a fragment by code and never get a null value.

Remove Fragment Page from ViewPager in Android

I'm trying to dynamically add and remove Fragments from a ViewPager, adding works without any problems, but removing doesn't work as expected.
Everytime I want to remove the current item, the last one gets removed.
I also tried to use an FragmentStatePagerAdapter or return POSITION_NONE in the adapter's getItemPosition method.
What am I doing wrong?
Here's a basic example:
MainActivity.java
public class MainActivity extends FragmentActivity implements TextProvider {
private Button mAdd;
private Button mRemove;
private ViewPager mPager;
private MyPagerAdapter mAdapter;
private ArrayList<String> mEntries = new ArrayList<String>();
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mEntries.add("pos 1");
mEntries.add("pos 2");
mEntries.add("pos 3");
mEntries.add("pos 4");
mEntries.add("pos 5");
mAdd = (Button) findViewById(R.id.add);
mRemove = (Button) findViewById(R.id.remove);
mPager = (ViewPager) findViewById(R.id.pager);
mAdd.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View view) {
addNewItem();
}
});
mRemove.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View view) {
removeCurrentItem();
}
});
mAdapter = new MyPagerAdapter(this.getSupportFragmentManager(), this);
mPager.setAdapter(mAdapter);
}
private void addNewItem() {
mEntries.add("new item");
mAdapter.notifyDataSetChanged();
}
private void removeCurrentItem() {
int position = mPager.getCurrentItem();
mEntries.remove(position);
mAdapter.notifyDataSetChanged();
}
#Override
public String getTextForPosition(int position) {
return mEntries.get(position);
}
#Override
public int getCount() {
return mEntries.size();
}
private class MyPagerAdapter extends FragmentPagerAdapter {
private TextProvider mProvider;
public MyPagerAdapter(FragmentManager fm, TextProvider provider) {
super(fm);
this.mProvider = provider;
}
#Override
public Fragment getItem(int position) {
return MyFragment.newInstance(mProvider.getTextForPosition(position));
}
#Override
public int getCount() {
return mProvider.getCount();
}
}
}
TextProvider.java
public interface TextProvider {
public String getTextForPosition(int position);
public int getCount();
}
MyFragment.java
public class MyFragment extends Fragment {
private String mText;
public static MyFragment newInstance(String text) {
MyFragment f = new MyFragment(text);
return f;
}
public MyFragment() {
}
public MyFragment(String text) {
this.mText = text;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View root = inflater.inflate(R.layout.fragment, container, false);
((TextView) root.findViewById(R.id.position)).setText(mText);
return root;
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<Button
android:id="#+id/add"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="add new item" />
<Button
android:id="#+id/remove"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="remove current item" />
<android.support.v4.view.ViewPager
android:id="#+id/pager"
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1" />
</LinearLayout>
fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="#+id/position"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:textSize="35sp" />
</LinearLayout>

The ViewPager doesn't remove your fragments with the code above because it loads several views (or fragments in your case) into memory. In addition to the visible view, it also loads the view to either side of the visible one. This provides the smooth scrolling from view to view that makes the ViewPager so cool.
To achieve the effect you want, you need to do a couple of things.
Change the FragmentPagerAdapter to a FragmentStatePagerAdapter. The reason for this is that the FragmentPagerAdapter will keep all the views that it loads into memory forever. Where the FragmentStatePagerAdapter disposes of views that fall outside the current and traversable views.
Override the adapter method getItemPosition (shown below). When we call mAdapter.notifyDataSetChanged(); the ViewPager interrogates the adapter to determine what has changed in terms of positioning. We use this method to say that everything has changed so reprocess all your view positioning.
And here's the code...
private class MyPagerAdapter extends FragmentStatePagerAdapter {
//... your existing code
#Override
public int getItemPosition(Object object){
return PagerAdapter.POSITION_NONE;
}
}

The solution by Louth was not enough to get things working for me, as the existing fragments were not getting destroyed. Motivated by this answer, I found that the solution is to override the getItemId(int position) method of FragmentPagerAdapter to give a new unique ID whenever there has been a change in the expected position of a Fragment.
Source Code:
private class MyPagerAdapter extends FragmentPagerAdapter {
private TextProvider mProvider;
private long baseId = 0;
public MyPagerAdapter(FragmentManager fm, TextProvider provider) {
super(fm);
this.mProvider = provider;
}
#Override
public Fragment getItem(int position) {
return MyFragment.newInstance(mProvider.getTextForPosition(position));
}
#Override
public int getCount() {
return mProvider.getCount();
}
//this is called when notifyDataSetChanged() is called
#Override
public int getItemPosition(Object object) {
// refresh all fragments when data set changed
return PagerAdapter.POSITION_NONE;
}
#Override
public long getItemId(int position) {
// give an ID different from position when position has been changed
return baseId + position;
}
/**
* Notify that the position of a fragment has been changed.
* Create a new ID for each position to force recreation of the fragment
* #param n number of items which have been changed
*/
public void notifyChangeInPosition(int n) {
// shift the ID returned by getItemId outside the range of all previous fragments
baseId += getCount() + n;
}
}
Now, for example if you delete a single tab or make some change to the order, you should call notifyChangeInPosition(1) before calling notifyDataSetChanged(), which will ensure that all the Fragments will be recreated.
Why this solution works
Overriding getItemPosition():
When notifyDataSetChanged() is called, the adapter calls the notifyChanged() method of the ViewPager which it is attached to. The ViewPager then checks the value returned by the adapter's getItemPosition() for each item, removing those items which return POSITION_NONE (see the source code) and then repopulating.
Overriding getItemId():
This is necessary to prevent the adapter from reloading the old fragment when the ViewPager is repopulating. You can easily understand why this works by looking at the source code for instantiateItem() in FragmentPagerAdapter.
final long itemId = getItemId(position);
// Do we already have this fragment?
String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);
} else {
fragment = getItem(position);
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,
makeFragmentName(container.getId(), itemId));
}
As you can see, the getItem() method is only called if the fragment manager finds no existing fragments with the same Id. To me it seems like a bug that the old fragments are still attached even after notifyDataSetChanged() is called, but the documentation for ViewPager does clearly state that:
Note this class is currently under early design and development. The API will likely change in later updates of the compatibility library, requiring changes to the source code of apps when they are compiled against the newer version.
So hopefully the workaround given here will not be necessary in a future version of the support library.

my working solution to remove fragment page from view pager
public class MyFragmentAdapter extends FragmentStatePagerAdapter {
private ArrayList<ItemFragment> pages;
public MyFragmentAdapter(FragmentManager fragmentManager, ArrayList<ItemFragment> pages) {
super(fragmentManager);
this.pages = pages;
}
#Override
public Fragment getItem(int index) {
return pages.get(index);
}
#Override
public int getCount() {
return pages.size();
}
#Override
public int getItemPosition(Object object) {
int index = pages.indexOf (object);
if (index == -1)
return POSITION_NONE;
else
return index;
}
}
And when i need to remove some page by index i do this
pages.remove(position); // ArrayList<ItemFragment>
adapter.notifyDataSetChanged(); // MyFragmentAdapter
Here it is my adapter initialization
MyFragmentAdapter adapter = new MyFragmentAdapter(getSupportFragmentManager(), pages);
viewPager.setAdapter(adapter);

The fragment must be already removed but the issue was viewpager save state
Try
myViewPager.setSaveFromParentEnabled(false);
Nothing worked but this solved the issue !
Cheers !

I had the idea of simply copy the source code from android.support.v4.app.FragmentPagerAdpater into a custom class named
CustumFragmentPagerAdapter. This gave me the chance to modify the instantiateItem(...) so that every time it is called, it removes / destroys the currently attached fragment before it adds the new fragment received from getItem() method.
Simply modify the instantiateItem(...) in the following way:
#Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
final long itemId = getItemId(position);
// Do we already have this fragment?
String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
// remove / destroy current fragment
if (fragment != null) {
mCurTransaction.remove(fragment);
}
// get new fragment and add it
fragment = getItem(position);
mCurTransaction.add(container.getId(), fragment, makeFragmentName(container.getId(), itemId));
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
}

You can combine both for better :
private class MyPagerAdapter extends FragmentStatePagerAdapter {
//... your existing code
#Override
public int getItemPosition(Object object){
if(Any_Reason_You_WantTo_Update_Positions) //this includes deleting or adding pages
return PagerAdapter.POSITION_NONE;
}
else
return PagerAdapter.POSITION_UNCHANGED; //this ensures high performance in other operations such as editing list items.
}

I had some problems with FragmentStatePagerAdapter.
After removing an item:
there was another item used for a position (an item which did not belong to the position but to a position next to it)
or some fragment was not loaded (there was only blank background visible on that page)
After lots of experiments, I came up with the following solution.
public class SomeAdapter extends FragmentStatePagerAdapter {
private List<Item> items = new ArrayList<Item>();
private boolean removing;
#Override
public Fragment getItem(int position) {
ItemFragment fragment = new ItemFragment();
Bundle args = new Bundle();
// use items.get(position) to configure fragment
fragment.setArguments(args);
return fragment;
}
#Override
public int getCount() {
return items.size();
}
#Override
public int getItemPosition(Object object) {
if (removing) {
return PagerAdapter.POSITION_NONE;
}
Item item = getItemOfFragment(object);
int index = items.indexOf(item);
if (index == -1) {
return POSITION_NONE;
} else {
return index;
}
}
public void addItem(Item item) {
items.add(item);
notifyDataSetChanged();
}
public void removeItem(int position) {
items.remove(position);
removing = true;
notifyDataSetChanged();
removing = false;
}
}
This solution only uses a hack in case of removing an item. Otherwise (e.g. when adding an item) it retains the cleanliness and performance of an original code.
Of course, from the outside of the adapter, you call only addItem/removeItem, no need to call notifyDataSetChanged().

For future readers!
Now you can use ViewPager2 for dynamically adding, removing fragment from the viewpager.
Quoting form API reference
ViewPager2 replaces ViewPager, addressing most of its predecessor’s
pain-points, including right-to-left layout support, vertical
orientation, modifiable Fragment collections, etc.
Take look at MutableCollectionFragmentActivity.kt in googlesample/android-viewpager2 for an example of adding, removing fragments dynamically from the viewpager.
For your information:
Articles:
Exploring the ViewPager2
Look deep into ViewPager2
API reference
Release notes
Samples Repo: https://github.com/googlesamples/android-viewpager2

Louth's answer works fine. But I don't think always return POSITION_NONE is a good idea. Because POSITION_NONE means that fragment should be destroyed and a new fragment will be created.
You can check that in dataSetChanged function in the source code of ViewPager.
if (newPos == PagerAdapter.POSITION_NONE) {
mItems.remove(i);
i--;
... not related code
mAdapter.destroyItem(this, ii.position, ii.object);
So I think you'd better use an arraylist of weakReference to save all the fragments you have created. And when you add or remove some page, you can get the right position from your own arraylist.
public int getItemPosition(Object object) {
for (int i = 0; i < mFragmentsReferences.size(); i ++) {
WeakReference<Fragment> reference = mFragmentsReferences.get(i);
if (reference != null && reference.get() != null) {
Fragment fragment = reference.get();
if (fragment == object) {
return i;
}
}
}
return POSITION_NONE;
}
According to the comments, getItemPosition is Called when the host view is attempting to determine if an item's position has changed. And the return value means its new position.
But this is not enought. We still have an important step to take.
In the source code of FragmentStatePagerAdapter, there is an array named "mFragments" caches the fragments which are not destroyed. And in instantiateItem function.
if (mFragments.size() > position) {
Fragment f = mFragments.get(position);
if (f != null) {
return f;
}
}
It returned the cached fragment directly when it find that cached fragment is not null. So there is a problem. From example, let's delete one page at position 2, Firstly, We remove that fragment from our own reference arraylist. so in getItemPosition it will return POSITION_NONE for that fragment, and then that fragment will be destroyed and removed from "mFragments".
mFragments.set(position, null);
Now the fragment at position 3 will be at position 2. And instantiatedItem with param position 3 will be called. At this time, the third item in "mFramgents" is not null, so it will return directly. But actually what it returned is the fragment at position 2. So when we turn into page 3, we will find an empty page there.
To work around this problem. My advise is that you can copy the source code of FragmentStatePagerAdapter into your own project, and when you do add or remove operations, you should add and remove elements in the "mFragments" arraylist.
Things will be simpler if you just use PagerAdapter instead of FragmentStatePagerAdapter. Good Luck.

add or remove fragment in viewpager dynamically.
Call setupViewPager(viewPager) on activity start.
To load different fragment call setupViewPagerCustom(viewPager).
e.g. on button click call: setupViewPagerCustom(viewPager);
private void setupViewPager(ViewPager viewPager)
{
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFrag(new fragmnet1(), "HOME");
adapter.addFrag(new fragmnet2(), "SERVICES");
viewPager.setAdapter(adapter);
}
private void setupViewPagerCustom(ViewPager viewPager)
{
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFrag(new fragmnet3(), "Contact us");
adapter.addFrag(new fragmnet4(), "ABOUT US");
viewPager.setAdapter(adapter);
}
//Viewpageradapter, handles the views
static class ViewPagerAdapter extends FragmentStatePagerAdapter
{
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager){
super(manager);
}
#Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
#Override
public int getCount() {
return mFragmentList.size();
}
#Override
public int getItemPosition(Object object){
return PagerAdapter.POSITION_NONE;
}
public void addFrag(Fragment fragment, String title){
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
#Override
public CharSequence getPageTitle(int position){
return mFragmentTitleList.get(position);
}
}

Try this solution. I have used databinding for binding view. You can use common "findViewById()" function.
public class ActCPExpense extends BaseActivity implements View.OnClickListener, {
private static final String TAG = ActCPExpense.class.getSimpleName();
private Context mContext;
private ActCpLossBinding mBinding;
private ViewPagerAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
try {
setContentView(R.layout.act_cp_loss);
mBinding = DataBindingUtil.setContentView(this, R.layout.act_cp_loss);
mContext = ActCPExpense.this;
initViewsAct();
} catch (Exception e) {
LogUtils.LOGE(TAG, e);
}
}
private void initViewsAct() {
adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(FragmentCPPayee.newInstance(), "Title");
mBinding.viewpager.setAdapter(adapter);
mBinding.tab.setViewPager(mBinding.viewpager);
}
#Override
public boolean onOptionsItemSelected(MenuItem itemActUtility) {
int i = itemActUtility.getItemId();
if (i == android.R.id.home) {
onBackPressed();
}
return super.onOptionsItemSelected(itemActUtility);
}
#Override
public void onClick(View view) {
super.onClick(view);
int id = view.getId();
if (id == R.id.btnAdd) {
addFragment();
} else if (id == R.id.btnDelete) {
removeFragment();
}
}
private void addFragment(){
adapter.addFragment(FragmentCPPayee.newInstance("Title");
adapter.notifyDataSetChanged();
mBinding.tab.setViewPager(mBinding.viewpager);
}
private void removeFragment(){
adapter.removeItem(mBinding.viewpager.getCurrentItem());
mBinding.tab.setViewPager(mBinding.viewpager);
}
class ViewPagerAdapter extends FragmentStatePagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
#Override
public int getItemPosition(#NonNull Object object) {
return PagerAdapter.POSITION_NONE;
}
#Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
#Override
public int getCount() {
return mFragmentList.size();
}
public void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
public void removeItem(int pos) {
destroyItem(null, pos, mFragmentList.get(pos));
mFragmentList.remove(pos);
mFragmentTitleList.remove(pos);
adapter.notifyDataSetChanged();
mBinding.viewpager.setCurrentItem(pos - 1, false);
}
#Override
public CharSequence getPageTitle(int position) {
return "Title " + String.valueOf(position + 1);
}
}
}

I added a function "clearFragments" and I used that function to clear adapter before setting the new fragments. This calls the proper remove actions of Fragments. My pagerAdapter class:
private class ChartPagerAdapter extends FragmentPagerAdapter{
private ArrayList<Fragment> fragmentList;
ChartPagerAdapter(FragmentManager fm){
super(fm);
fragmentList = new ArrayList<>();
}
void setFragments(ArrayList<? extends Fragment> fragments){
fragmentList.addAll(fragments);
}
void clearFragments(){
for(Fragment fragment:fragmentList)
getChildFragmentManager().beginTransaction().remove(fragment).commit();
fragmentList.clear();
}
#Override
public Fragment getItem(int i) {
return fragmentList.get(i);
}
#Override
public int getCount() {
return fragmentList.size();
}
}

i solved this problem by these steps
1- use FragmentPagerAdapter
2- in each fragment create a random id
fragment.id = new Random().nextInt();
3- override getItemPosition in adapter
#Override
public int getItemPosition(#NonNull Object object) {
return PagerAdapter.POSITION_NONE;
}
4-override getItemId in adapter
#Override
public long getItemId(int position) {
return mDatasetFragments.get(position).id;
}
5- now delete code is
adapter.mDatasetFragments.remove(< item to delete position >);
adapter.notifyDataSetChanged();
this worked for me i hope help

My final version code, fixed ALL bugs. It took me 3 days
Updated 2020/07/18:
I had changed a lot of the source code and fix so many bugs, but I don't promise it still work today.
https://github.com/lin1987www/FragmentBuilder/blob/master/commonLibrary/src/main/java/android/support/v4/app/FragmentStatePagerAdapterFix.java
public class FragmentStatePagerAdapterFix extends PagerAdapter {
private static final String TAG = FragmentStatePagerAdapterFix.class.getSimpleName();
private static final boolean DEBUG = false;
private WeakReference<FragmentActivity> wrFragmentActivity;
private WeakReference<Fragment> wrParentFragment;
private final FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction = null;
protected ArrayList<Fragment> mFragments = new ArrayList<>();
protected ArrayList<FragmentState> mFragmentStates = new ArrayList<>();
protected ArrayList<String> mFragmentTags = new ArrayList<>();
protected ArrayList<String> mFragmentClassNames = new ArrayList<>();
protected ArrayList<Bundle> mFragmentArgs = new ArrayList<>();
private Fragment mCurrentPrimaryItem = null;
private boolean[] mTempPositionChange;
#Override
public int getCount() {
return mFragmentClassNames.size();
}
public FragmentActivity getFragmentActivity() {
return wrFragmentActivity.get();
}
public Fragment getParentFragment() {
return wrParentFragment.get();
}
public FragmentStatePagerAdapterFix(FragmentActivity activity) {
mFragmentManager = activity.getSupportFragmentManager();
wrFragmentActivity = new WeakReference<>(activity);
wrParentFragment = new WeakReference<>(null);
}
public FragmentStatePagerAdapterFix(Fragment fragment) {
mFragmentManager = fragment.getChildFragmentManager();
wrFragmentActivity = new WeakReference<>(fragment.getActivity());
wrParentFragment = new WeakReference<>(fragment);
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass) {
add(fragClass, null, null);
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass, Bundle args) {
add(fragClass, args, null);
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass, String tag) {
add(fragClass, null, tag);
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass, Bundle args, String tag) {
add(fragClass, args, tag, getCount());
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass, Bundle args, String tag, int position) {
mFragments.add(position, null);
mFragmentStates.add(position, null);
mFragmentTags.add(position, tag);
mFragmentClassNames.add(position, fragClass.getName());
mFragmentArgs.add(position, args);
mTempPositionChange = new boolean[getCount()];
}
public void remove(int position) {
if (position < getCount()) {
mTempPositionChange = new boolean[getCount()];
for (int i = position; i < mTempPositionChange.length; i++) {
mTempPositionChange[i] = true;
}
mFragments.remove(position);
mFragmentStates.remove(position);
mFragmentTags.remove(position);
mFragmentClassNames.remove(position);
mFragmentArgs.remove(position);
}
}
public void clear(){
mFragments.clear();
mFragmentStates.clear();
mFragmentTags.clear();
mFragmentClassNames.clear();
mFragmentArgs.clear();
}
#Override
public void startUpdate(ViewGroup container) {
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Fragment fragment;
// If we already have this item instantiated, there is nothing
// to do. This can happen when we are restoring the entire pager
// from its saved state, where the fragment manager has already
// taken care of restoring the fragments we previously had instantiated.
fragment = mFragments.get(position);
if (fragment != null) {
return fragment;
}
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
FragmentState fs = mFragmentStates.get(position);
if (fs != null) {
fragment = fs.instantiate(getFragmentActivity(), getParentFragment());
// Fix bug
// http://stackoverflow.com/questions/11381470/classnotfoundexception-when-unmarshalling-android-support-v4-view-viewpagersav
if (fragment.mSavedFragmentState != null) {
fragment.mSavedFragmentState.setClassLoader(fragment.getClass().getClassLoader());
}
}
if (fragment == null) {
fragment = Fragment.instantiate(getFragmentActivity(), mFragmentClassNames.get(position), mFragmentArgs.get(position));
}
if (DEBUG) {
Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
}
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
mFragments.set(position, fragment);
mFragmentStates.set(position, null);
mCurTransaction.add(container.getId(), fragment, mFragmentTags.get(position));
return fragment;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
Fragment fragment = (Fragment) object;
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
if (DEBUG) {
Log.v(TAG, "Removing item #" + position + ": f=" + object
+ " v=" + ((Fragment) object).getView());
}
if (position < getCount()) {
FragmentState fragmentState = new FragmentState(fragment);
Fragment.SavedState savedState = mFragmentManager.saveFragmentInstanceState(fragment);
if (savedState != null) {
fragmentState.mSavedFragmentState = savedState.mState;
}
mFragmentStates.set(position, fragmentState);
mFragments.set(position, null);
}
mCurTransaction.remove(fragment);
}
#Override
public void setPrimaryItem(ViewGroup container, int position, Object object) {
Fragment fragment = (Fragment) object;
if (fragment != mCurrentPrimaryItem) {
if (mCurrentPrimaryItem != null) {
mCurrentPrimaryItem.setMenuVisibility(false);
mCurrentPrimaryItem.setUserVisibleHint(false);
}
if (fragment != null) {
fragment.setMenuVisibility(true);
fragment.setUserVisibleHint(true);
}
mCurrentPrimaryItem = fragment;
}
}
#Override
public void finishUpdate(ViewGroup container) {
if (mCurTransaction != null) {
mCurTransaction.commitAllowingStateLoss();
mCurTransaction = null;
mFragmentManager.executePendingTransactions();
// Fix: Fragment is added by transaction. BUT didn't add to FragmentManager's mActive.
for (Fragment fragment : mFragments) {
if (fragment != null) {
fixActiveFragment(mFragmentManager, fragment);
}
}
}
}
#Override
public boolean isViewFromObject(View view, Object object) {
return ((Fragment) object).getView() == view;
}
#Override
public Parcelable saveState() {
Bundle state = null;
// 目前顯示的 Fragments
for (int i = 0; i < mFragments.size(); i++) {
Fragment f = mFragments.get(i);
if (f != null && f.isAdded()) {
if (state == null) {
state = new Bundle();
}
String key = "f" + i;
mFragmentManager.putFragment(state, key, f);
}
}
if (mFragmentStates.size() > 0) {
if (state == null) {
state = new Bundle();
}
FragmentState[] fs = new FragmentState[mFragmentStates.size()];
mFragmentStates.toArray(fs);
state.putParcelableArray("states_fragment", fs);
}
return state;
}
#Override
public void restoreState(Parcelable state, ClassLoader loader) {
if (state != null) {
Bundle bundle = (Bundle) state;
bundle.setClassLoader(loader);
Parcelable[] fs = bundle.getParcelableArray("states_fragment");
mFragments.clear();
mFragmentStates.clear();
mFragmentTags.clear();
mFragmentClassNames.clear();
mFragmentArgs.clear();
if (fs != null) {
for (int i = 0; i < fs.length; i++) {
FragmentState fragmentState = (FragmentState) fs[i];
mFragmentStates.add(fragmentState);
if (fragmentState != null) {
mFragmentArgs.add(fragmentState.mArguments);
mFragmentTags.add(fragmentState.mTag);
mFragmentClassNames.add(fragmentState.mClassName);
} else {
mFragmentArgs.add(null);
mFragmentTags.add(null);
mFragmentClassNames.add(null);
}
mFragments.add(null);
}
}
Iterable<String> keys = bundle.keySet();
for (String key : keys) {
if (key.startsWith("f")) {
int index = Integer.parseInt(key.substring(1));
Fragment f = mFragmentManager.getFragment(bundle, key);
if (f != null) {
f.setMenuVisibility(false);
mFragments.set(index, f);
mFragmentArgs.set(index, f.mArguments);
mFragmentTags.set(index, f.mTag);
mFragmentClassNames.set(index, f.getClass().getName());
} else {
Log.w(TAG, "Bad fragment at key " + key);
}
}
}
// If restore will change
notifyDataSetChanged();
}
}
public static void fixActiveFragment(FragmentManager fragmentManager, Fragment fragment) {
FragmentManagerImpl fm = (FragmentManagerImpl) fragmentManager;
if (fm.mActive != null) {
int index = fragment.mIndex;
Fragment origin = fm.mActive.get(index);
if (origin != null) {
if ((origin.mIndex != fragment.mIndex) || !(origin.equals(fragment))) {
Log.e(TAG,
String.format("fixActiveFragment: Not Equal! Origin: %s %s, Fragment: %s $s",
origin.getClass().getName(), origin.mIndex,
fragment.getClass().getName(), fragment.mIndex
));
}
}
fm.mActive.set(index, fragment);
}
}
// Fix
// http://stackoverflow.com/questions/10396321/remove-fragment-page-from-viewpager-in-android
#Override
public int getItemPosition(Object object) {
int index = mFragments.indexOf(object);
if (index < 0) {
return PagerAdapter.POSITION_NONE;
}
boolean isPositionChange = mTempPositionChange[index];
int result = PagerAdapter.POSITION_UNCHANGED;
if (isPositionChange) {
result = PagerAdapter.POSITION_NONE;
}
return result;
}
}

2020 now.
Simple add this to PageAdapter:
override fun getItemPosition(`object`: Any): Int {
return PagerAdapter.POSITION_NONE
}

You could just override the destroyItem method
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
fragmentManager.beginTransaction().remove((Fragment) object).commitNowAllowingStateLoss();
}

I hope this can help what you want.
private class MyPagerAdapter extends FragmentStatePagerAdapter {
//... your existing code
#Override
public int getItemPosition(Object object){
return PagerAdapter.POSITION_UNCHANGED;
}
}

FragmentPagerAdapter is not removing items (Fragments) correctly

I have implemented the FragmentPagerAdapter and and using a List<Fragment> to hold all fragments for my ViewPager to display. On addItem() I simply add an instantiated Fragment and then call notifyDataSetChanged(). I am not sure if this is necessary or not.
My problem simply...
start with fragment 1
[Fragment 1]
add new Fragment 2
[Fragment 1] [Fragment 2]
remove Fragment 2
[Fragment 1]
add new Fragment 3
[Fragment 1] [Fragment 2]
When adding new fragments everything seems great. Once I remove a fragment and then add a newly instantiated fragment the old fragment is still displayed. When i go a .getClass.getName() it is giving me Fragment 3's name however I still see Fragment 2.
I believe this might be an issue with instantiateItem() or such but I thought the adapter was to handle that for us. Any suggestions would be great.
adapter code...
public class MyPagerAdapter extends FragmentPagerAdapter {
public final ArrayList<Fragment> screens2 = new ArrayList<Fragment>();
private Context context;
public MyPagerAdapter(FragmentManager fm, Context context) {
super(fm);
this.context = context;
}
public void removeType(String name){
for(Fragment f: screens2){
if(f.getClass().getName().contains(name)){ screens2.remove(f); return; }
}
this.notifyDataSetChanged();
}
public boolean addSt(String tag, Class<?> clss, Bundle args){
if(clss==null) return false;
if(!clss.getName().contains("St")) return false;
if(!args.containsKey("cId")) return false;
boolean has = false;
boolean hasAlready = false;
for(Fragment tab: screens2){
if(tab.getClass().getName().contains("St")){
has = true;
if(tab.getArguments().containsKey("cId"))
if(tab.getArguments().getLong("cId") == args.getLong("cId")){
hasAlready = true;
}
if(!hasAlready){
// exists but is different so replace
screens2.remove(tab);
this.addScreen(tag, clss, args, C.PAGE_ST);
// if returned true then it notifies dataset
return true;
}
}
hasAlready = false;
}
if(!has){
// no st yet exist in adapter
this.addScreen(tag, clss, args, C.PAGE_ST);
return true;
}
return false;
}
public boolean removeCCreate(){
this.removeType("Create");
return false;
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE; //To make notifyDataSetChanged() do something
}
public void addCCreate(){
this.removeCCreate();
Log.w("addding c", " ");
this.addScreen("Create C", CreateCFragment.class, null, C.PAGE_CREATE_C);
}
public void addScreen(String tag, Class<?> clss, Bundle args, int type){
if(clss!=null){
screens2.add(Fragment.instantiate(context, clss.getName(), args));
}
}
#Override
public int getCount() {
return screens2.size();
}
#Override
public Fragment getItem(int position) {
return screens2.get(position);
}
}
I realize the code uses some "ghetto" means of determining the fragment type however I wrote this code strictly for testing functionality. Any help or ideas would be great as it seems that not many people ventured into the world of FragmentPagerAdapters.

I got same problem,and my solution was overring the method "destroyItem" as following.
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
FragmentManager manager = ((Fragment)object).getFragmentManager();
FragmentTransaction trans = manager.beginTransaction();
trans.remove((Fragment)object);
trans.commit();
}
It's work for me,does anybody have another solutions?
Updated:
I found those code made Fragment removed unnecessary,so I added a condition to avoid it.
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
if (position >= getCount()) {
FragmentManager manager = ((Fragment) object).getFragmentManager();
FragmentTransaction trans = manager.beginTransaction();
trans.remove((Fragment) object);
trans.commit();
}
}

Updated this post and included my solution (if someone can improve let me know)
Ok i've now solved my problem in a hackish way, but yeah it's working ;). If someone can improve my solution please let me know. For my new solution i now use a CustomFragmentStatePagerAdapter but it doesn't save the state like it should and stores all the Fragments in a list. This can cause a memory problem if the user has more than 50 fragments, like the normal FragmentPagerAdapter does. It would be great if someone can add the State-thing back to my solution without removing my fixes. Thanks.
So here's my CustomFragmentStatePagerAdapter.java
package com.tundem.webLab.Adapter;
import java.util.ArrayList;
import android.os.Bundle;
import android.os.Parcelable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.PagerAdapter;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
public abstract class CustomFragmentStatePagerAdapter extends PagerAdapter {
private static final String TAG = "FragmentStatePagerAdapter";
private static final boolean DEBUG = false;
private final FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction = null;
public ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>();
public ArrayList<Fragment> mFragments = new ArrayList<Fragment>();
private Fragment mCurrentPrimaryItem = null;
public CustomFragmentStatePagerAdapter(FragmentManager fm) {
mFragmentManager = fm;
}
/**
* Return the Fragment associated with a specified position.
*/
public abstract Fragment getItem(int position);
#Override
public void startUpdate(ViewGroup container) {}
#Override
public Object instantiateItem(ViewGroup container, int position) {
// If we already have this item instantiated, there is nothing
// to do. This can happen when we are restoring the entire pager
// from its saved state, where the fragment manager has already
// taken care of restoring the fragments we previously had instantiated.
// DONE Remove of the add process of the old stuff
/* if (mFragments.size() > position) { Fragment f = mFragments.get(position); if (f != null) { return f; } } */
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
Fragment fragment = getItem(position);
if (DEBUG)
Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
if (mSavedState.size() > position) {
Fragment.SavedState fss = mSavedState.get(position);
if (fss != null) {
try // DONE: Try Catch
{
fragment.setInitialSavedState(fss);
} catch (Exception ex) {
// Schon aktiv (kA was das heißt xD)
}
}
}
while (mFragments.size() <= position) {
mFragments.add(null);
}
fragment.setMenuVisibility(false);
mFragments.set(position, fragment);
mCurTransaction.add(container.getId(), fragment);
return fragment;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
Fragment fragment = (Fragment) object;
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
mCurTransaction.remove(fragment);
/*if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } if (DEBUG) Log.v(TAG, "Removing item #" + position + ": f=" + object + " v=" + ((Fragment)
* object).getView()); while (mSavedState.size() <= position) { mSavedState.add(null); } mSavedState.set(position, mFragmentManager.saveFragmentInstanceState(fragment));
* mFragments.set(position, null); mCurTransaction.remove(fragment); */
}
#Override
public void setPrimaryItem(ViewGroup container, int position, Object object) {
Fragment fragment = (Fragment) object;
if (fragment != mCurrentPrimaryItem) {
if (mCurrentPrimaryItem != null) {
mCurrentPrimaryItem.setMenuVisibility(false);
}
if (fragment != null) {
fragment.setMenuVisibility(true);
}
mCurrentPrimaryItem = fragment;
}
}
#Override
public void finishUpdate(ViewGroup container) {
if (mCurTransaction != null) {
mCurTransaction.commitAllowingStateLoss();
mCurTransaction = null;
mFragmentManager.executePendingTransactions();
}
}
#Override
public boolean isViewFromObject(View view, Object object) {
return ((Fragment) object).getView() == view;
}
#Override
public Parcelable saveState() {
Bundle state = null;
if (mSavedState.size() > 0) {
state = new Bundle();
Fragment.SavedState[] fss = new Fragment.SavedState[mSavedState.size()];
mSavedState.toArray(fss);
state.putParcelableArray("states", fss);
}
for (int i = 0; i < mFragments.size(); i++) {
Fragment f = mFragments.get(i);
if (f != null) {
if (state == null) {
state = new Bundle();
}
String key = "f" + i;
mFragmentManager.putFragment(state, key, f);
}
}
return state;
}
#Override
public void restoreState(Parcelable state, ClassLoader loader) {
if (state != null) {
Bundle bundle = (Bundle) state;
bundle.setClassLoader(loader);
Parcelable[] fss = bundle.getParcelableArray("states");
mSavedState.clear();
mFragments.clear();
if (fss != null) {
for (int i = 0; i < fss.length; i++) {
mSavedState.add((Fragment.SavedState) fss[i]);
}
}
Iterable<String> keys = bundle.keySet();
for (String key : keys) {
if (key.startsWith("f")) {
int index = Integer.parseInt(key.substring(1));
Fragment f = mFragmentManager.getFragment(bundle, key);
if (f != null) {
while (mFragments.size() <= index) {
mFragments.add(null);
}
f.setMenuVisibility(false);
mFragments.set(index, f);
} else {
Log.w(TAG, "Bad fragment at key " + key);
}
}
}
}
}
}
Here's my normal FragmentAdapter.java
package com.tundem.webLab.Adapter;
import java.util.LinkedList;
import java.util.List;
import android.support.v4.app.FragmentManager;
import com.tundem.webLab.fragments.BaseFragment;
import com.viewpagerindicator.TitleProvider;
public class FragmentAdapter extends CustomFragmentStatePagerAdapter implements TitleProvider {
public List<BaseFragment> fragments = new LinkedList<BaseFragment>();
private int actPage;
public FragmentAdapter(FragmentManager fm) {
super(fm);
}
public void setActPage(int actPage) {
this.actPage = actPage;
}
public void addItem(BaseFragment fragment) {
// TODO if exists don't open / change to that tab
fragments.add(fragment);
}
public BaseFragment getActFragment() {
return getItem(getActPage());
}
public int getActPage() {
return actPage;
}
#Override
public BaseFragment getItem(int position) {
if (position < getCount()) {
return fragments.get(position);
} else
return null;
}
#Override
public int getCount() {
return fragments.size();
}
#Override
public String getTitle(int position) {
return fragments.get(position).getTitle();
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
}
And this is the way i delete a Fragment. (I know it's a bit more than only .remove() ). Be free to improve my solution, you can also add this code somewhere in the adapter so yeah. It's up to the user who tries to implement this. I use this in my TabHelper.java (A class which handles all tab operations like delete, add, ...)
int act = Cfg.mPager.getCurrentItem();
Cfg.mPager.removeAllViews();
Cfg.mAdapter.mFragments.remove(act);
try {
Cfg.mAdapter.mSavedState.remove(act);
} catch (Exception ex) {/* Already removed */}
try {
Cfg.mAdapter.fragments.remove(act);
} catch (Exception ex) {/* Already removed */}
Cfg.mAdapter.notifyDataSetChanged();
Cfg.mIndicator.notifyDataSetChanged();
Description of the Cfg. thing. I save the reference to those objects in a cfg, class so i can always use them without the need of a special Factory.java ...
Yeah. i hope i was able to help. Feel free to improve this, but let me know so i can improve my code too.
Thanks.
If i missed any code let me know.
My old answer also works but only if you have different Fragments. FileFragment, WebFragment, ... Not if you use one of those fragmenttypes twice.
I got it pseudo working for now. It's a really dirty solution and i'm still searching for a better one. Please help.
I changed the code, where i delete a tab to this one:
public static void deleteActTab()
{
//We set this on the indicator, NOT the pager
int act = Cfg.mPager.getCurrentItem();
Cfg.mAdapter.removeItem(act);
List<BaseFragment> frags = new LinkedList<BaseFragment>();
frags = Cfg.mAdapter.fragments;
Cfg.mPager = (ViewPager)Cfg.act.findViewById(R.id.pager);
Cfg.mPager.setAdapter(Cfg.mAdapter);
Cfg.mIndicator.setViewPager(Cfg.mPager);
Cfg.mAdapter.fragments = frags;
if(act > 0)
{
Cfg.mPager.setCurrentItem(act-1);
Cfg.mIndicator.setCurrentItem(act-1);
}
Cfg.mIndicator.notifyDataSetChanged();
}
If someone can improve this code let me know. If someone can tell us the real answer for that problem. please add it here. There are many many people who experience this issue. I added a reputation of 50 for the one who solve it. I can also give a donation for the one who solve it.
Thanks

Maybe this answer helps you.
Use FragmentStatePagerAdapter instead of FragmentPagerAdapter.
Because FragmentPagerAdapter does not destory the views. For more information read this answer.

Taking "the best of both worlds" (I mean the answers by #Tericky Shih and #mikepenz) we have it short and simple:
public class MyPagerAdapter extends FragmentPagerAdapter {
public ArrayList<Fragment> fragments = new ArrayList<Fragment>();
...
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
super.destroyItem(container, position, object);
if (position >= getCount()) fm.beginTransaction().remove((Fragment) object).commit();
}
#Override
public int getItemPosition(Object object) {
if (fragments.contains(object)) return fragments.indexOf(object);
else return POSITION_NONE;
}
}
The main difference is that if some fragment is not changed you don't have to destroy its view and don't have to return POSITION_NONE for it. At the same time, I've encountered a situation when ViewPager was holding a reference to an item which was already destroyed, therefore the check if (fragments.contains(object)) helps to determine if that item is not needed anymore.

I had a situation similar to yours. I recently needed to add and remove Fragments from the ViewPager. In the first mode, I have Fragments 0, 1, and 2 and in the second mode I have Fragments 0 and 3. I want Fragment 0 to be same for both modes and hold over information.
All I needed to do was override FragmentPagerAdapter.getItemId to make sure that I returned a unique number for each different Fragment - the default is to return "position". I also had to set the adapter in the ViewPager again - a new instance will work but I set it back to the same instance. Setting the adapter results in the ViewPager removing all the views and trying to add them again.
However, the trick is that the adapter only calls getItem when it wants to instantiate the Fragment - not every time it shows it. This is because they are cached and looks them up by the "position" returned by getItemId.
Imagine you have three Fragments (0, 1 and 2) and you want to remove "1".
If you return "position" for getItemId then removing Fragment 1 will not work because when you try to show Fragment 2 after deleting Fragment 1 the pager/adapter will think it's already got the Fragment for that "position" and will continue to display Fragment 1.
FYI: I tried notifyDataSetChanged instead of setting the adapter but it didn't work for me.
First, the getItemId override example and what I did for my getItem:
public class SectionsPagerAdapter extends FragmentPagerAdapter
{
...
#Override
public long getItemId(int position)
{
// Mode 1 uses Fragments 0, 1 and 2. Mode 2 uses Fragments 0 and 3
if ( mode == 2 && position == 1 )
return 3;
return position;
}
#Override
public Fragment getItem(int position)
{
if ( mode == 1 )
{
switch (position)
{
case 0:
return <<fragment 0>>;
case 1:
return <<fragment 1>>;
case 2:
return <<fragment 2>>;
}
}
else // Mode 2
{
switch (position)
{
case 0:
return <<fragment 0>>;
case 1:
return <<fragment 3>>;
}
}
return null;
}
}
Now the change of mode:
private void modeChanged(int newMode)
{
if ( newMode == mode )
return;
mode = newMode;
// Calling mSectionsPagerAdapter.notifyDataSetChanged() is not enough here
mViewPager.setAdapter(mSectionsPagerAdapter);
}

Didn't work out for me. My solution was put FragmentStatePagerAdapter.java in my project, renamed to FragmentStatePagerAdapter2.java.
In destroyItem(), I changed a little based on error logs. From
// mFragments.set(position, null);
to
if (position < mFragments.size())mFragments.remove(position);
Maybe you don't have the same problem, just check the log.Hope this helps someone!

After a lot of trying, i got it to work so that it removes or attaches a third fragment at the end position correctly.
Object fragments[] = new Object[3];
int mItems = 2;
MyAdapter mAdapter;
ViewPager mPager;
public void addFragment(boolean bool) {
mAdapter.startUpdate(mPager);
if (!bool) {
mAdapter.destroyItem(mPager, 2, fragments[2]);
mItems = 2;
fNach = false;
}
else if (bool && !fNach){
mItems = 3;
mAdapter.instantiateItem(mPager,2);
fNach = true;
}
mAdapter.finishUpdate(mPager);
mAdapter.notifyDataSetChanged();
}
public class MyAdapter extends FragmentPagerAdapter {
MyAdapter(FragmentManager fm) {
super(fm);
}
#Override
public int getCount() {
return mItems;
}
#Override
public CharSequence getPageTitle(int position) {
... (code for the PagerTitleStrip)
}
#Override
public Fragment getItem(int position) {
Fragment f = null;
switch (position) {
case 0:
f = new Fragment1();
break;
case 1:
f = new Fragment2();
break;
case 2:
f = new Fragment3();
break;
}
return f;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Object o = super.instantiateItem(container,position);
fragments[position] = o;
return o;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
super.destroyItem(container, position, object);
System.out.println("Destroy item " + position);
if (position >= getCount()) {
FragmentManager manager = ((Fragment) object).getFragmentManager();
FragmentTransaction ft = manager.beginTransaction();
ft.remove((Fragment) object);
ft.commit();
}
}
}
Some clarification: to get the object reference to call destroyItem, i stored the objects returned from instantiateItem in an Array. When you are adding or removing fragments, you have to announce it with startUpdate, finishUpdate and notifyDataSetChanged. The number of items have to be changed manually, for adding you increase it and instantiate it, getItem creates it then. For deletion, you call destroyItem, and in this code, it is essential the position >= mItems, because destroyItem is also called if a fragment goes out of the cache. You don't want to delete it then. The only thing which doesn't work is the swiping animation. After removing the last page, the "cannot swipe left" animation is not restored correctly on the new last page. If you swipe it, a blank page is shown and it bounces back.

The real problem is that FragmentPagerAdapter uses the position of the fragment in your list as ID. So if you add a new List or simply remove items "instantiateItem" item will find different fragments for new items in list...
#Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
final long itemId = getItemId(position);
// Do we already have this fragment?
String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);
} else {
fragment = getItem(position);
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,
makeFragmentName(container.getId(), itemId));
}
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
}
and
private static String makeFragmentName(int viewId, long id) {
return "android:switcher:" + viewId + ":" + id;
}
and
* Return a unique identifier for the item at the given position.
* <p>
* <p>The default implementation returns the given position.
* Subclasses should override this method if the positions of items can change.</p>
*
* #param position Position within this adapter
* #return Unique identifier for the item at position
*/
public long getItemId(int position) {
return position;
}

I have been having this same issue until I dawned on me, I was creating my PagerView from within another Fragment and not the main activity.
My solution was to pass the ChildFragment Manager into the constructor of the Fragment(State)PagerAdapter and not the Fragment Manager of the parent Fragment.
Using the ChildFragmentManager all the Fragments created by the ViewPagerAdapter are cleaned up automatically when the parent Fragment is destroyed.