My application has to swipe in between fragments when a button is pressed. If I was hosting swipe tab and view pager inside an activity, I would do something like this.
((ParentActivityName) getActivity()).setCurrentItem(2, true);
Now I have a parent Fragment that hosts the slide tabs. It has the following method to set current child Fragment to viewpager.
public void setCurrentItem (int item, boolean smoothScroll) {
pager.setCurrentItem(item, smoothScroll);
}
On Click of "Next" button in one of the sliding tab Fragments, I am trying to call the method as
new FragUserRegistration().setCurrentItem(1,true);
But is simply returning a null object reference error. Any help would be much appreciated.
I worked it out simply by calling viewpager from parent Fragment to each sliding tab fragments and then the associated setCurrentItem method.
viewPager = (ViewPager)getActivity().findViewById(R.id.pager);
viewPager.setCurrentItem(int position, true);
//four swipe-able fragments so position - -> 1-3 (total count 4)
I am not sure where your click happens to set the current item.
Maybe you'll find this useful:
Your MainFragment:
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
//init view
MainViewPageAdapter mainViewPageAdapter = new MainViewPageAdapter(getChildFragmentManager());
yourViewPager.setAdapter(mainViewPageAdapter);
return view;
}
private class MainViewPageAdapter extends FragmentStatePagerAdapter {
private static final int MAX_COUNT = 2;
public MainViewPageAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
Fragment fragment = null;
switch (position) {
case 1:
fragment = YourChildFragmentOne.getInstance();
break;
case 2:
fragment = YourChildFragmentTwo.getInstance();
break;
}
return fragment;
}
#Override
public int getCount() {
return MAX_COUNT;
}
}
In your ChildFragment(s):
(or create an abstract ChildFragment, which handles the click listener and create two instances of the abstract one)
private OnChildFragmentClickListener mClickListener;
#Override
public void onAttach(Context context) {
super.onAttach(context);
mClickListener = (OnChildFragmentClickListener) getParentFragment();
}
//call somewhere in your ChildFragment mClickListener.onChildFragClick(index);
public interface OnChildFragmentClickListener{
void onChildFragClick(int index);
}
Now let your MainFragment implement OnChildFragmentClickListener and call there:
#Override
public void onChildFragClick(int index){
yourViewPager.setCurrentItem(index);
}
Related
I have three Fragments attached to ViewPager. If i am Fragment1, and i have a button on Fragment1, i want on button click of that 'Fragment', access the Fragment3 but on the same time if i slide the page,i don't want to access the Fragment3. while sliding i want to access only up to Fragment2. How can i do this.
TabPagerAdapter.java:-
public class TabPagerAdapter extends FragmentStatePagerAdapter
{
public TabPagerAdapter(FragmentManager fragmentManager)
{
super(fragmentManager);
}
#Override
public Fragment getItem(int position)
{
switch (position)
{
case 0:
return new Fragment1();
case 1:
return new Fragment2();
case 2:
return new Fragment3();
}
return null;
}
#Override
public int getCount()
{
return 3;
}
I have implemented something very similar: Previously I had four fragments in my ViewPager, but then decided that I want to integrate two of those fragments more intimately by reducing the number of fragment that I can reach by sliding and switching back and forth between two fragments by using a button. The implementation took me a while, though. I did not manage to mess with the index of my fragmentList properly. In the end, the trick was to take out those two fragments from the ViewPager altogether and add a HolderFragment instead. Within this fragment I implemented the fragment transaction for hiding one and showing the other fragment.
Here is the code from my HolderFragment:
public class HolderFragment extends Fragment {
private Context context;
private Fragment currentFragment;
#Override
public void onAttach(Context context) {
super.onAttach(context);
this.context = context;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.fragment_holder, container, false);
OneFragment oneFragment =
(OneFragment) Fragment.instantiate(context, OneFragment.class.getName());
OtherFragment otherFragment =
(OtherFragment) Fragment.instantiate(context, OtherFragment.class.getName());
// oneFragment selected on view creation
FragmentManager fm = this.getChildFragmentManager();
fm.beginTransaction().add(R.id.holder_fragment_holder, oneFragment).commit();
fm.beginTransaction().add(R.id.holder_fragment_holder, otherFragment).hide(mediaFragment)
.commit();
currentFragment = oneFragment;
return view;
}
public void switchFragments(Fragment fragment) {
if (!fragment.equals(currentFragment)) {
this.getChildFragmentManager().beginTransaction().hide(currentFragment).commit();
currentFragment = fragment;
this.getChildFragmentManager().beginTransaction().show(currentFragment).commit();
}
}
}
Then, whenever the switch button is pressed just call holderFragment.switchFragments(oneFragment) or holderFragment.switchFragments(otherFragment) from the activity that holds the ViewPager (and a reference to the HolderFragment).
Try this
mViewPager.setCurrentItem(your_position, true);
I have an app that uses SectionsPagerAdapter to show 3 fragments within an activity (this part was automatically generated by Android Studio after selecting a tabbed activity). Right now, this is how I select what fragment to show:
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
if (position == 0) {
return new Fragment1();
} else if (position == 1) {
return new Fragment2();
} else {
return new Fragment3();
}
}
#Override
public int getCount() {
return 3;
}
}
I would like my app to start on Fragment 2 (i.e. position 1), to allow the user to either swipe right to go back to the first fragment, or to swipe left to move on to the next fragment.
How can I set the position to start at? I couldn't find any method to set the position number, is there one or should I do this another way?
If it helps, this is my onCreateView method of my MainActivity class:
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
I don't think an Activity has onCreateView method. Its a method of a fragment. Your activity will have public void onCreate(Bundle savedInstanceState)
If my assumptions are not wrong, in the layout of your main activity you will have a android.support.v4.view.ViewPager.
and in your code you might declare your view pager variable and set the SectionsPagerAdapter to it. After that just do viewPager.setCurrentItem(1);
How can I set the position to start at?
Call setCurrentItem() on the ViewPager.
I have an activity with 3 fragments (A, B, C). Fragment A consists of a ViewPager with 2 ListFragments. The user can tap on an item in any of the listfragments and by doing so, goes to fragment B.
In fragment A I do:
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
pagerAdapter = new PagerAdapter(getActivity().getSupportFragmentManager());
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragmentA, container, false);
vpPager = (ViewPager)view.findViewById(R.id.vpPager);
vpPager.setOffscreenPageLimit(2);
vpPager.setAdapter(pagerAdapter);
vpPager.addOnPageChangeListener(this);
return view;
}
And the PagerAdapter is as follows:
private class PagerAdapter extends FragmentPagerAdapter {
private final ListFragment1 lf1 = ListFragment1 .newInstance();
private final ListFragment2 lf2 = ListFragment2 .newInstance();
public PagerAdapter(android.support.v4.app.FragmentManager fm) {
super(fm);
}
#Override
public android.support.v4.app.Fragment getItem(int position) {
switch (position) {
case 0: return lf1;
case 1: return lf2;
default: return null;
}
}
}
The first time the activity is shown, the viewpager list fragments are displayed correctly.
The 2 viewpager fragments load data from a db, and I do this only once (when the fragments are created).
The user can tap on an item and fragment B is displayed. If the user presses Back, fragment A is shown. However the list fragments are not shown (already an instance of them still exists).
Could it be that the view has been destroyed, even though instances exist?
What is wrong here? Is there a better approach?
EDIT
If I use newInstance in the pager adapter, I get an IllegalStateException: not attached to activity. This is because I start an async task as follows:
#Override
public void onPageSelected(int position) {
Fragment fragment = pagerAdapter.getItem(position);
if (fragment instanceof IPagedFragment) {
((IPagedFragment) fragment).onShown();
}
}
And onShown is:
#Override
public void onShown() {
myTask= new MyTask();
myTask.execute((Void)null);
}
When can I start the task so that I can be 100% sure that the fragment is attached to the activity and that the view has been created (I need to get listview, etc. from the layout).
You have to use ChildFragmentManager like below.
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
pagerAdapter = new PagerAdapter(getChildFragmentManager()); //here used child fragment manager
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragmentA, container, false);
vpPager = (ViewPager)view.findViewById(R.id.vpPager);
vpPager.setOffscreenPageLimit(2);
vpPager.setAdapter(pagerAdapter);
vpPager.addOnPageChangeListener(this);
return view;
}
It works like charm in my code with viewpager and fragment.
Just now I solved it after struggling for whole day, by using getChildFragmentManager()
pass this as a parameter to the pagerAdapter. and it will work.
while using pagerAdapter in fragment use :
PagerAdapter adapter = new PagerAdapter(getChildFragmentManager());
and in case of activity use getFragmentManager()
PagerAdapter adapter = new PagerAdapter(getFragmentManager());
You're creating ListFragment1 and ListFragment2 using the Activity FragmentManager, while you should use the Fragment FragmentManager. So, modify the pagerAdapter = new PagerAdapter(getActivity().getSupportFragmentManager()); with pagerAdapter = new PagerAdapter(getChildFragmentManager());. In this way, the fragments of the view pager will be 'bound' to the fragment hosting the viewpager. Moreover, you should not keep any reference to fragments inside the viewpager: it's something that Android already manage. Try with:
private class PagerAdapter extends FragmentPagerAdapter {
public PagerAdapter(android.support.v4.app.FragmentManager fm) {
super(fm);
}
#Override
public android.support.v4.app.Fragment getItem(int position) {
switch (position) {
case 0: return ListFragment1.newInstance();
case 1: return ListFragment2.newInstance();
default: return null;
}
}
}
By the way, the vpPager.setOffscreenPageLimit(2); is unuseful since you have just 2 pages and this is a method that I've never used even when I have many fragments to manage, since it requires memory.
About your update: remove any logic related to ViewPager handling the fragment. If you need to start an AsyncTask within your Fragment, you can do it using one of the methods of Fragment lifecycle: onResume(), onCreateView() and so on.
class IPagedFragment extends Fragment {
public void onResume() {
super.onResume();
myTask= new MyTask();
myTask.execute((Void)null);
}
}
and please, remove the private final ListFragment1 lf1 = ListFragment1 .newInstance();. Trust me, it's not a good idea since you have a strong reference to your Fragments.
I've built a simple project that you can use as reference implementation. You can download the source code from my dropbox.
use getChildFragmentManager() instead of supportFragmentManager()
If any of the solutions above doesn't work, you can try a workaround by posting (delayed) to the pager view instance an additional notifyDataSetChanged call of the adapter:
vpPager.post(new Runnable() {
#Override
public void run() {
pagerAdapter.notifyDataSetChanged();
}
});
or
vpPager.postDelayed(new Runnable() {
#Override
public void run() {
pagerAdapter.notifyDataSetChanged();
}
}, 100 /* you have to find out the best delay time by trying/adjusting */);
Try overriding the getItemPosition method in your FragmentPagerAdapter:
#Override
public int getItemPosition(Object object) {
return PagerAdapter.POSITION_NONE;
}
If you experience this with Kotlin, it will be like this.
val fragmentAdapter = FragmentPageAdapter(childFragmentManager)
You shouldn't keep references to fragments in your FragmentPagerAdapter. You should always call newInstance in getItem() call, for example:
#Override
public android.support.v4.app.Fragment getItem(int position) {
switch (position) {
case 0: return ListFragment1.newInstance();
case 1: return ListFragment2.newInstance();
default: return null;
}
}
The data you load from the database should be stored in the fragment itself. The adapter will restore the state of fragments (setOffscreenPageLimit(2)).
You are losing your fragments because the items (fragments) are instantiated by the FragmentManager you provide, and it creates fragments based on tags. So it can happen that it creates a new instance of the fragment you already keep, just with different tag.
See FragmentPagerAdapter source code (check instantiateItem() method):
https://android.googlesource.com/platform/frameworks/support/+/refs/heads/master/v13/java/android/support/v13/app/FragmentPagerAdapter.java
Also see this answer:
keep instances of fragments inside FragmentPagerAdapter
On PagerAdapter class override the method setPrimaryItem,
which is called when there's a change in the pager, i would give it a shot.
I would create something like :
private class PagerAdapter extends FragmentPagerAdapter {
private final ListFragment1 lf1 = ListFragment1 .newInstance();
private final ListFragment2 lf2 = ListFragment2 .newInstance();
public PagerAdapter(android.support.v4.app.FragmentManager fm) {
super(fm);
}
#Override
public android.support.v4.app.Fragment getItem(int position) {
switch (position) {
case 0: return lf1;
case 1: return lf2;
default: return null;
}
}
#Override
public int getCount() {
return 2;
}
#Override
public void setPrimaryItem(ViewGroup container, int position, Object object) {
super.setPrimaryItem(container, position, object);
if (position == 0)
lf1.updateUI(); //Refresh what you need on this fragment
else if (position == 1)
lf2.updateUI();
}
}
You're missing getCount() as well.
I'm not sure offscreen has any use, but its probably not an issue. vpPager.setOffscreenPageLimit(2)
One more thing, i would also remove vpPager.addOnPageChangeListener(this), there's no use for this, an it might cause you some issues.
Whatever you need to do, you can pull it off without it, by overriding the pagination, you might "ruin" some of the standard pagination(since the super isn't called)
Current I have a ViewPager which have 3 different tabs(Peer, Sync and Share).
In the Peer fragment, it contain a ListView with clickable items. OnItemClick I wish to open a new fragment which will display the detail of the selected item,
But I am not sure how to properly implement this functionality...
Activity:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.file_sharing_activity);
// Tabs stuff ...
this.tabsAdapter = new TabsPagerAdapter(this.getSupportFragmentManager());
viewPager = (ViewPager) findViewById(R.id.pager);
viewPager.setAdapter(this.tabsAdapter);
// Create tabs bar
final ActionBar actionBar = getActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Create tab fragments
this.peerListFragment = new PeerListFragment();
this.syncFragment = new SyncFragment();
this.shareFragment = new ShareFragment();
// Create tabs
actionBar.addTab(actionBar.newTab().setText("Peers").setTabListener(this.peerListFragment));
actionBar.addTab(actionBar.newTab().setText("Sync").setTabListener(this.syncFragment));
actionBar.addTab(actionBar.newTab().setText("Share").setTabListener(this.shareFragment));
viewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int position) {
// When swiping between pages, select the
// corresponding tab.
getActionBar().setSelectedNavigationItem(position);
}
});
try {
ProgramController.getInstance().initializeProgram(this);
} catch (Exception e) {}
}
TabPagerAdapter:
private class TabsPagerAdapter extends FragmentPagerAdapter{
public TabsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return peerListFragment;
case 1:
return syncFragment;
case 2:
return shareFragment;
default:
return null;
}
}
#Override
public int getCount() {
return NB_TABS;
}
}
PeerListFragment
public class PeerListFragment extends Fragment implements ActionBar.TabListener{
ListView peerListView;
public PeerListFragment(){
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_peer_list, container, false);
peerListView = (ListView) view.findViewById(R.id.list_peer);
PeerListAdapter adapter = new PeerListAdapter(getActivity());
peerListView.setAdapter(adapter);
peerListView.setOnItemClickListener(new OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
//Display detail fragment here
}
});
return view;
}
In general, you would have a method on your Activity that would be called from onItemClick() to display the detail view, i,e, showDetail(itemId). The Activity would actually handle the transition to the detail view.
Now, since your ViewPager is in an Activity and not a Fragment, you have two choices:
Have a DetailActivity that is started with an Intent from your current Activity. (Easiest option, but less flexible for tablets)
Rewrite your Activity to put your view with the ViewPager in a Fragment. Then the Activity would replace the current fragment that has the ViewPager with the detail fragment. (Harder option, but you can display side-by-side in a tablet).
Right now, your ViewPager is in your activity layout. In order to make the fragments work, your activity layout would just have one or two child layouts which function as fragment containers, then the ViewPager would go into a fragment layout.
Problem
A Fragment is not reattached to its hosting ViewPager after returning from another fragment.
Situation
One Activity hosting a Fragment whose layout holds a ViewPager (PageListFragment in the example below). The ViewPager is populated by a FragmentStateViewPagerAdapter. The single Fragments hosted inside the pager (PageFragment in the example below) can open sub page lists, containing a new set of pages.
Behaviour
All works fine as long as the back button is not pressed. As soon as the user closes one of the sub PageLists the previous List is recreated, but without the Page that was displayed previously. Swiping through the other pages on the parent PageList still works.
Code
A sample application can be found on github:
Activity
public class MainActivity extends FragmentActivity {
private static final String CURRENT_FRAGMENT = MainActivity.class.getCanonicalName() + ".CURRENT_FRAGMENT";
public static final String ARG_PARENTS = "Parents";
public void goInto(String mHostingLevel, String mPosition) {
Fragment hostingFragment = newHostingFragment(mHostingLevel, mPosition);
addFragment(hostingFragment);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addBaseFragment();
}
private void addBaseFragment() {
Fragment hostingFragment = newHostingFragment("", "");
addFragment(hostingFragment);
}
private Fragment newHostingFragment(String mHostingLevel, String oldPosition) {
Fragment hostingFragment = new PageListFragment();
Bundle args = new Bundle();
args.putString(ARG_PARENTS, mHostingLevel + oldPosition +" > ");
hostingFragment.setArguments(args);
return hostingFragment;
}
private void addFragment(Fragment hostingFragment) {
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.fragmentSpace, hostingFragment, CURRENT_FRAGMENT);
transaction.addToBackStack(null);
transaction.commit();
}
}
PageListFragment
public class PageListFragment extends Fragment {
private String mParentString;
public PageListFragment() {
// Required empty public constructor
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_hosting, container, false);
}
#Override
public void onResume() {
mParentString = getArguments().getString(MainActivity.ARG_PARENTS);
ViewPager viewPager = (ViewPager) getView().findViewById(R.id.viewPager);
viewPager.setAdapter(new SimpleFragmentStatePagerAdapter(getFragmentManager(),mParentString));
super.onResume();
}
private static class SimpleFragmentStatePagerAdapter extends FragmentStatePagerAdapter {
private String mHostingLevel;
public SimpleFragmentStatePagerAdapter(FragmentManager fm, String hostingLevel) {
super(fm);
this.mHostingLevel = hostingLevel;
}
#Override
public android.support.v4.app.Fragment getItem(int position) {
PageFragment pageFragment = new PageFragment();
Bundle args = new Bundle();
args.putString(MainActivity.ARG_PARENTS, mHostingLevel);
args.putInt(PageFragment.ARG_POSITION, position);
pageFragment.setArguments(args);
return pageFragment;
}
#Override
public int getCount() {
return 5;
}
}
}
PageFragment
public class PageFragment extends Fragment {
public static final String ARG_POSITION = "Position";
private String mHostingLevel;
private int mPosition;
public PageFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View contentView = inflater.inflate(R.layout.fragment_page, container, false);
setupTextView(contentView);
setupButton(contentView);
return contentView;
}
private void setupTextView(View contentView) {
mPosition = getArguments().getInt(ARG_POSITION);
mHostingLevel = getArguments().getString(MainActivity.ARG_PARENTS);
TextView text = (TextView) contentView.findViewById(R.id.textView);
text.setText("Parent Fragments " + mHostingLevel + " \n\nCurrent Fragment "+ mPosition);
}
private void setupButton(View contentView) {
Button button = (Button) contentView.findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
openNewLevel();
}
});
}
protected void openNewLevel() {
MainActivity activity = (MainActivity) getActivity();
activity.goInto(mHostingLevel, Integer.toString(mPosition));
}
}
After a lengthy investigation it turns out to be a problem with the fragment manager.
When using a construct like the one above the fragment transaction to reattach the fragment to the page list is silently discarded. It is basically the same problem that causes a
java.lang.IllegalStateException: Recursive entry to executePendingTransactions
when trying to alter the fragments inside the FragmentPager.
The same solution, as for problems with this error, is also applicable here. When constructing the FragmentStatePagerAdapter supply the correct child fragment manager.
Instead of
viewPager.setAdapter(new SimpleFragmentStatePagerAdapter(getFragmentManager(),mParentString));
do
viewPager.setAdapter(new SimpleFragmentStatePagerAdapter(getChildFragmentManager(),mParentString));
See also: github
What Paul has failed to mention is, if you use getChildFragmentManager, then you will suffer the "blank screen on back pressed" issue.
The hierarchy in my case was:
MainActivity->MainFragment->TabLayout+ViewPager->AccountsFragment+SavingsFragment+InvestmentsFragment etc.
The problem I had was that I couldn't use childFragmentManagerfor the reason that a click on the item Account view (who resides inside one of the Fragments of the ViewPager) needed to replace MainFragment i.e. the entire screen.
Using MainFragments host Fragment i.e. passing getFragmentManager() enabled the replacing, BUT when popping the back-stack, I ended up with this screen:
This was apparent also by looking at the layout inspector where the ViewPager is empty.
Apparently looking at the restored Fragments you would notice that their View is restored but will not match the hierarchy of the popped state. In order to make the minimum impact and not force a re-creation of the Fragments I re-wrote FragmentStatePagerAdapter with the following changes:
I copied the entire code of FragmentStatePagerAdapter and changed
#NonNull
#Override
public Object instantiateItem(#NonNull 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.
if (mFragments.size() > position) {
Fragment f = mFragments.get(position);
if (f != null) {
return f;
}
}
...
}
with
#NonNull
#Override
public Object instantiateItem(#NonNull 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.
if (mFragments.size() > position) {
Fragment f = mFragments.get(position);
if (f != null) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
mCurTransaction.detach(f);
mCurTransaction.attach(f);
return f;
}
}
...
}
This way I am effectively making sure that that the restored Fragments are re-attached to the ViewPager.
Delete all page fragments, enabling them to be re-added later
The page fragments are not attached when you return to the viewpager screen as the FragmentStatePagerAdapter is not re-connecting them. As a work-around, delete all the fragments in the viewpager after popbackstack() is called, which will allow them to be re-added by your initial code.
[This example is written in Kotlin]
//Clear all fragments from the adapter before they are re-added.
for (i: Int in 0 until adapter.count) {
val item = childFragmentManager.findFragmentByTag("f$i")
if (item != null) {
adapter.destroyItem(container!!, i, item)
}
}