Update ViewPager dynamically

Question

I can t update the content in ViewPager   What is the correct usage of methods instantiateItem   and getItem   in FragmentPagerAdapter class   I was using only getItem   to instantiate and return my fragments    Override public Fragment getItem int position        return new MyFragment context  paramters       This worked well  Except I can t change the content   So I found this  ViewPager PagerAdapter not updating the View      My approach is to use the setTag   method for any instantiated view in the instantiateItem   method    Now I want to implement instantiateItem   to do that  But I don t know what I have to return  the type is Object  and what is the relation with getItem int position    I read the reference         public abstract Fragment getItem  int position       Return the Fragment associated with a specified position    public Object instantiateItem  ViewGroup container  int position       Create the page for the given position  The adapter is responsible for adding the view to the container given here  although it only must ensure this is done by the time it returns from finishUpdate ViewGroup     Parameters      container   The containing View in which the page will be shown    position    The page position to be instantiated       Returns      Returns an Object representing the new page  This does not need to be a View  but can be some other container of the page       but I still don t get it   Here s my code  I m using support package v4   ViewPagerTest   public class ViewPagerTest extends FragmentActivity       private ViewPager pager      private MyFragmentAdapter adapter         Override     public void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           setContentView R layout pager1            pager    ViewPager findViewById R id slider            String   data     page1    page2    page3    page4    page5    page6             adapter   new MyFragmentAdapter getSupportFragmentManager    6  this  data           pager setAdapter adapter              Button findViewById R id button   setOnClickListener new OnClickListener                  Override             public void onClick View v                    reload                                         private void reload             String   data     changed1    changed2    changed3    changed4    changed5    changed6              adapter   new MyFragmentAdapter getSupportFragmentManager    6  this  data           adapter setData data           adapter notifyDataSetChanged            pager invalidate               pager setCurrentItem 0             MyFragmentAdapter  class MyFragmentAdapter extends FragmentPagerAdapter       private int slideCount      private Context context      private String   data       public MyFragmentAdapter FragmentManager fm  int slideCount  Context context  String   data            super fm           this slideCount   slideCount          this context   context          this data   data              Override     public Fragment getItem int position            return new MyFragment data position   context               Override     public int getCount             return slideCount             public void setData String   data            this data   data              Override     public int getItemPosition Object object            return POSITION NONE            MyFragment  public final class MyFragment extends Fragment       private String text       public MyFragment String text  Context context            this text   text              Override     public View onCreateView LayoutInflater inflater  ViewGroup container  Bundle savedInstanceState            View view   inflater inflate R layout slide  null             TextView view findViewById R id text   setText text            return view            Here is also somebody with a similar problem  no answers http   www mail-archive com android-developers googlegroups com msg200477 html

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This solution won t work for everyone  but in my case  every Fragment in my ViewPager is a different class  and only one of them ever exist at a time    With this constraint  this solution is safe and should be safe to use in production   private void updateFragment Item item         List lt Fragment gt  fragments   getSupportFragmentManager   getFragments        for  Fragment fragment   fragments             if  fragment instanceof MyItemFragment  amp  amp  fragment isVisible                    MyItemFragment  fragment  update item                        If you have multiple versions of the same fragment  you can use this same strategy to call methods on those fragments to determine if it is the fragment you wish to update

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Instead of returning POSITION NONE from getItemPosition   and causing full view recreation  do this     call this method to update fragments in ViewPager dynamically public void update UpdateData xyzData        this updateData   xyzData      notifyDataSetChanged        Override public int getItemPosition Object object        if  object instanceof UpdateableFragment              UpdateableFragment  object  update updateData               don t return POSITION NONE  avoid fragment recreation       return super getItemPosition object       Your fragments should implement UpdateableFragment interface   public class SomeFragment extends Fragment implements     UpdateableFragment        Override     public void update UpdateData xyzData                this method will be called for every fragment in viewpager             so check if update is for this fragment          if forMe xyzData                   do whatever you want to update your UI                      and the interface   public interface UpdateableFragment      public void update UpdateData xyzData       Your data class   public class UpdateData         whatever you want here

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When using FragmentPagerAdapter or FragmentStatePagerAdapter  it is best to deal solely with getItem   and not touch instantiateItem   at all  The instantiateItem  -destroyItem  -isViewFromObject   interface on PagerAdapter is a lower-level interface that FragmentPagerAdapter uses to implement the much simpler getItem   interface   Before getting into this  I should clarify that      if you want to switch out the actual fragments that are being displayed  you need to avoid FragmentPagerAdapter and use   FragmentStatePagerAdapter    An earlier version of this answer made the mistake of using FragmentPagerAdapter for its example - that won t work because FragmentPagerAdapter never destroys a fragment after it s been displayed the first time   I don t recommend the setTag   and findViewWithTag   workaround provided in the post you linked  As you ve discovered  using setTag   and findViewWithTag   doesn t work with fragments  so it s not a good match   The right solution is to override getItemPosition    When notifyDataSetChanged   is called  ViewPager calls getItemPosition   on all the items in its adapter to see whether they need to be moved to a different position or removed    By default  getItemPosition   returns POSITION UNCHANGED  which means   This object is fine where it is  don t destroy or remove it   Returning POSITION NONE fixes the problem by instead saying   This object is no longer an item I m displaying  remove it   So it has the effect of removing and recreating every single item in your adapter    This is a completely legitimate fix  This fix makes notifyDataSetChanged behave like a regular Adapter without view recycling  If you implement this fix and performance is satisfactory  you re off to the races  Job done   If you need better performance  you can use a fancier getItemPosition   implementation  Here s an example for a pager creating fragments off of a list of strings   ViewPager pager      get my ViewPager        assume this actually has stuff in it final ArrayList lt String gt  titles   new ArrayList lt String gt      FragmentManager fm   getSupportFragmentManager    pager setAdapter new FragmentStatePagerAdapter fm        public int getCount             return titles size               public Fragment getItem int position            MyFragment fragment   new MyFragment            fragment setTitle titles get position            return fragment             public int getItemPosition Object item            MyFragment fragment    MyFragment item          String title   fragment getTitle            int position   titles indexOf title            if  position  gt   0                return position            else               return POSITION NONE                        With this implementation  only fragments displaying new titles will get displayed  Any fragments displaying titles that are still in the list will instead be moved around to their new position in the list  and fragments with titles that are no longer in the list at all will be destroyed   What if the fragment has not been recreated  but needs to be updated anyway  Updates to a living fragment are best handled by the fragment itself  That s the advantage of having a fragment  after all - it is its own controller  A fragment can add a listener or an observer to another object in onCreate    and then remove it in onDestroy    thus managing the updates itself  You don t have to put all the update code inside getItem   like you do in an adapter for a ListView or other AdapterView types   One last thing - just because FragmentPagerAdapter doesn t destroy a fragment doesn t mean that getItemPosition is completely useless in a FragmentPagerAdapter  You can still use this callback to reorder your fragments in the ViewPager  It will never remove them completely from the FragmentManager  though

User · Answer

I know am late for the Party  I ve fixed the problem by calling TabLayout setupWithViewPager myViewPager   just after FragmentPagerAdapter notifyDataSetChanged

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I slightly modified the solution provided by Bill Phillips to suit my needs  private class PagerAdapter extends FragmentStatePagerAdapter      Bundle oBundle      FragmentManager oFragmentManager      ArrayList lt Fragment gt  oPooledFragments   public PagerAdapter FragmentManager fm        super fm       oFragmentManager fm          Override public int getItemPosition Object object         Fragment oFragment  Fragment object      oPooledFragments new ArrayList lt  gt  oFragmentManager getFragments         if oPooledFragments contains oFragment           return POSITION NONE      else         return POSITION UNCHANGED             so that the getItemPosition   returns POSITION NONE only for those fragments which are currently in the FragmentManager when getItemPosition is called   Note that this FragmentStatePager and the ViewPager associated with it are contained in a Fragment not in a Activity

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I had a similar problem but don t want to trust on the existing solutions  hard coded tag names etc   and I couldn t make M-WaJeEh s solution work for me  Here is my solution   I keep references to the fragments created in getItem in an array  This works fine as long as the activity is not destroyed due to configurationChange or lack of memory or whatever  --  when coming back to the activity  fragments return to their last state without  getItem  being called again and thus without updating the array    To avoid this problem I implemented instantiateItem ViewGroup  int  and update my array there  like this            Override     public Object instantiateItem ViewGroup container  int position            Object o   super instantiateItem container  position           if o instanceof FragmentX               myFragments 0     FragmentX o           else if o instanceof FragmentY               myFragments 1     FragmentY o           else if o instanceof FragmentZ               myFragments 2     FragmentZ o                    return o          So  on the one hand I m happy that I found a solution that works for me and wanted to share it with you  but I also wanted to ask whether somebody else tried something similar and whether there is any reason why I shouldn t do it like that  So far it works very good for me

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Here is my implementation that incorporates the info from  Bill Phillips One gets fragment caching most of the time  except when the data has changed  Simple  and seems to work fine   MyFragmentStatePagerAdapter java  private boolean mIsUpdating   false  public void setIsUpdating boolean mIsUpdating            this mIsUpdating   mIsUpdating           Override public int getItemPosition  NonNull Object object         if  mIsUpdating            return POSITION NONE            else           return super getItemPosition object             MyActivity java  mAdapter setIsUpdating true   mAdapter notifyDataSetChanged    mAdapter setIsUpdating false

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Use FragmentStatePagerAdapter instead of FragmentPagerAdapter if you want to recreate or reload fragment on index basis  For example if you want to reload fragment other than FirstFragment  you can check instance and return position like this   public int getItemPosition Object item        if item instanceof FirstFragment          return 0            return POSITION NONE

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I use EventBus library to update Fragment content in ViewPager  The logic is simple  just like document of EventBus how to do  It is no need to control FragmentPagerAdapter instance  The code is here   1  Define events  Define which message which is needed to update     public class UpdateCountEvent       public final int count       public UpdateCountEvent int count            this count   count            2 Prepare subscribers  Write below code in the Fragment which is needed update    Override public void onStart         super onStart        EventBus getDefault   register this       Override public void onStop         EventBus getDefault   unregister this         super onStop       public void onEvent UpdateCountEvent event     get update message     Toast makeText getActivity    event count  Toast LENGTH SHORT  show        3 Post events  Write below code in other Activity or other Fragment which needs to update parameter        input update message EventBus getDefault   post new UpdateCountEvent count

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After hours of frustration while trying all the above solutions to overcome this problem and also trying many solutions on other similar questions like this  this and this which all FAILED with me to solve this problem and to make the ViewPager to destroy the old Fragment and fill the pager with the new Fragments  I have solved the problem as following   1  Make the ViewPager class to extends FragmentPagerAdapter as following    public class myPagerAdapter extends FragmentPagerAdapter     2  Create an Item for the ViewPager that store the title and the fragment as following   public class PagerItem   private String mTitle  private Fragment mFragment    public PagerItem String mTitle  Fragment mFragment        this mTitle   mTitle      this mFragment   mFragment    public String getTitle         return mTitle    public Fragment getFragment         return mFragment    public void setTitle String mTitle        this mTitle   mTitle     public void setFragment Fragment mFragment        this mFragment   mFragment         3  Make the constructor of the ViewPager take my FragmentManager instance to store it in my class as following   private FragmentManager mFragmentManager  private ArrayList lt PagerItem gt  mPagerItems   public MyPagerAdapter FragmentManager fragmentManager  ArrayList lt PagerItem gt  pagerItems        super fragmentManager       mFragmentManager   fragmentManager      mPagerItems   pagerItems      4  Create a method to re-set the adapter data with the new data by deleting all the previous fragment from the fragmentManager itself directly to make the adapter to set the new fragment from the new list again as following   public void setPagerItems ArrayList lt PagerItem gt  pagerItems        if  mPagerItems    null          for  int i   0  i  lt  mPagerItems size    i                  mFragmentManager beginTransaction   remove mPagerItems get i  getFragment    commit                  mPagerItems   pagerItems      5  From the container Activity or Fragment do not re-initialize the adapter with the new data  Set the new data through the method setPagerItems with the new data as following   ArrayList lt PagerItem gt  pagerItems   new ArrayList lt PagerItem gt         pagerItems add new PagerItem  Fragment1   new MyFragment1          pagerItems add new PagerItem  Fragment2   new MyFragment2           mPagerAdapter setPagerItems pagerItems       mPagerAdapter notifyDataSetChanged      I hope it helps

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for those who still face the same problem which i faced before when i have a ViewPager with 7 fragments  the default for these fragments to load the English content from API service but the problem here that i want to change the language from settings activity and after finish  settings activity i want ViewPager in main activity to refresh the fragments to match the language selection from the user and load the Arabic content if user chooses Arabic here what i did to work from the first time   1- You must use FragmentStatePagerAdapter as mentioned above   2- on mainActivity i override the onResume and did the following    if    mPagerAdapter    null         mPagerAdapter notifyDataSetChanged        3-i overrided the getItemPosition   in mPagerAdapter and make it return POSITION NONE    Override public int getItemPosition Object object        return POSITION NONE      works like charm

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I have lived same problem and I have searched too much times  Any answer given in stackoverflow or via google was not solution for my problem  My problem was easy  I have a list  I show this list with viewpager  When I add a new element to head of the list and I refresh the viewpager nothings changed  My final solution was very easy anybody can use  When a new element added to list and want to refresh the list  Firstly set viewpager adapter to null then recreate the adapter and set i to it to viewpager   myVPager setAdapter null   myFragmentAdapter   new MyFragmentAdapter getSupportFragmentManager   newList   myVPager setAdapter myFragmentAdapter     Be sure your adapter must extend FragmentStatePagerAdapter

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I have encountered this problem and finally solved it today  so I write down what I have learned and I hope it is helpful for someone who is new to Android s ViewPager and update as I do  I m using FragmentStatePagerAdapter in API level 17 and currently have just 2 fragments  I think there must be something not correct  please correct me  thanks     Serialized data has to be loaded into memory  This can be done using a CursorLoader AsyncTask Thread  Whether it s automatically loaded depends on your code  If you are using a CursorLoader  it s auto-loaded since there is a registered data observer  After you call viewpager setAdapter pageradapter   the adapter s getCount   is constantly called to build fragments  So if data is being loaded  getCount   can return 0  thus you don t need to create dummy fragments for no data shown  After the data is loaded  the adapter will not build fragments automatically since getCount   is still 0  so we can set the actually loaded data number to be returned by getCount    then call the adapter s notifyDataSetChanged    ViewPager begin to create fragments  just the first 2 fragments  by data in memory  It s done before notifyDataSetChanged   is returned  Then the ViewPager has the right fragments you need  If the data in the database and memory are both updated  write through   or just data in memory is updated  write back   or only data in the database is updated  In the last two cases if data is not automatically loaded from the database to memory  as mentioned above   The ViewPager and pager adapter just deal with data in memory  So when data in memory is updated  we just need to call the adapter s notifyDataSetChanged    Since the fragment is already created  the adapter s onItemPosition   will be called before notifyDataSetChanged   returns  Nothing needs to be done in getItemPosition    Then the data is updated

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For some reason none of the answers worked for me so I had to override the restoreState method without calling super in my fragmentStatePagerAdapter  Code   private class MyAdapter extends FragmentStatePagerAdapter            Rest of implementation        Override     public void restoreState Parcelable state  ClassLoader loader

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I ve gone through all the answers above and a number of others posts but still couldn t find something that worked for me  with different fragment types along with dynamically adding and removing tabs    FWIW following approach is what worked for me  in case anyone else has same issues      public class MyFragmentStatePageAdapter extends FragmentStatePagerAdapter       private static final String TAB1 TITLE    Tab 1       private static final String TAB2 TITLE    Tab 2       private static final String TAB3 TITLE    Tab 3        private ArrayList lt String gt  titles   new ArrayList lt  gt         private Map lt Fragment  Integer gt  fragmentPositions   new HashMap lt  gt           public MyFragmentStatePageAdapter FragmentManager fm            super fm               public void update boolean showTab1  boolean showTab2  boolean showTab3            titles clear             if  showTab1                titles add TAB1 TITLE                     if  showTab2                titles add TAB2 TITLE                     if  showTab3                titles add TAB3 TITLE                     notifyDataSetChanged                 Override     public int getCount             return titles size                Override     public Fragment getItem int position            Fragment fragment   null           String tabName   titles get position           if  tabName equals TAB1 TITLE                  fragment    Tab1Fragment newInstance              else if  tabName equals TAB2 TITLE                 fragment    Tab2Fragment newInstance              else if  tabName equals TAB3 TITLE                 fragment    Tab3Fragmen newInstance                          BaseFragment fragment  setTitle tabName           fragmentPositions put fragment  position           return fragment              Override     public CharSequence getPageTitle int position            return titles get position               Override     public int getItemPosition Object item            BaseFragment fragment    BaseFragment item          String title   fragment getTitle            int position   titles indexOf title            Integer fragmentPosition   fragmentPositions get item           if  fragmentPosition    null  amp  amp  position    fragmentPosition                return POSITION UNCHANGED            else               return POSITION NONE                        Override     public void destroyItem ViewGroup container  int position  Object object            super destroyItem container  position  object           fragmentPositions remove object

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This might be of help to someone - in my case when inserting a new page the view pager was asking for the position of an existing fragment twice  but not asking for the position of the new item  causing incorrect behaviour and data not displaying    Copy the source for for FragmentStatePagerAdapter  seems to have not been updated in ages   Override notifyDataSetChanged     Override public void notifyDataSetChanged         mFragments clear        super notifyDataSetChanged       Add a sanity check to destroyItem   to prevent crashes   if  position  lt  mFragments size          mFragments set position  null

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If you want to use FragmentStatePagerAdapter  please take a look at https   code google com p android issues detail can 2 amp start 0 amp num 100 amp q  amp colspec ID 20Type 20Status 20Owner 20Summary 20Stars amp groupby  amp sort  amp id 37990  There are issues with FragmentStatePagerAdapter that may or may not trouble your use case     Also  link has few solutions too  few may suit to your requirement

User · Answer

Try destroyDrawingCache   on ViewPager after notifyDataSetChanged   in your code

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You need change instantiateItem s mFragments element getItemPosition       if  mFragments size    gt  position            Fragment f   mFragments get position            if  f    null                int newPosition   getItemPosition f               if  newPosition    POSITION UNCHANGED                    return f                else if  newPosition    POSITION NONE                    mFragments set position  null                 else                   mFragments set newPosition  f                                   Based AndroidX FragmentStatePagerAdapter java  because mFragments s elements position do not change when calling notifyDataSetChanged     Source   https   github com cuichanghao infivt blob master library src main java cc cuichanghao library FragmentStatePagerChangeableAdapter java  Example  https   github com cuichanghao infivt blob master app src main java cc cuichanghao infivt MainActivityChangeablePager kt  You can run this project to confirm how to work  https   github com cuichanghao infivt

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I had been trying so many different approaches  none really sove my problem  Below are how I solve it with a mix of solutions provided by you all  Thanks everyone   class PagerAdapter extends FragmentPagerAdapter        public boolean flag refresh false       public PagerAdapter FragmentManager fm            super fm               Override     public Fragment getItem int page            FragmentsMain f          f new FragmentsMain            f page page          return f              Override     public int getCount             return 4              Override     public int getItemPosition Object item            int page    FragmentsMain item  page           if  page    0  amp  amp  flag refresh                flag refresh false              return POSITION NONE            else               return super getItemPosition item                         Override     public void destroyItem View container  int position  Object object               ViewPager  container  removeView  View  object             I only want to refresh page 0 after onResume      adapter new PagerAdapter getSupportFragmentManager      pager setAdapter adapter     Override protected void onResume         super onResume         if  adapter  null            adapter flag refresh true          adapter notifyDataSetChanged              In my FragmentsMain  there is public integer  page   which can tell me whether it is the page I want to refresh   public class FragmentsMain extends Fragment    private Cursor cursor  private static Context context  public int page -1

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Using ViewPager2 and FragmentStateAdapter  Updating data dynamically is supported by ViewPager2  There is an important note in the docs on how to get this working   Note  The DiffUtil utility class relies on identifying items by ID  If you are using ViewPager2 to page through a mutable collection  you must also override getItemId   and containsItem     emphasis mine   Based on ViewPager2 documentation and Android s Github sample project there are a few steps we need to take   Set up FragmentStateAdapter and override the following methods  getItemCount  createFragment  getItemId  and containsItem  note  FragmentStatePagerAdapter is not supported by ViewPager2   Attach adapter to ViewPager2  Dispatch list updates to ViewPager2 with DiffUtil  don t need to use DiffUtil  as seen in sample project     Example  private val items  List lt Int gt      get     viewModel items private val viewPager  ViewPager2   binding viewPager  private val adapter   object   FragmentStateAdapter this Fragment        override fun getItemCount     items size     override fun createFragment position  Int   Fragment   MyFragment       override fun getItemId position  Int   Long   items position  id     override fun containsItem itemId  Long   Boolean   items any   it id    itemId     viewPager adapter   adapter      private fun onDataChanged         DiffUtil          calculateDiff object   DiffUtil Callback                 override fun getOldListSize    Int   viewPager adapter itemCount             override fun getNewListSize    Int   viewModel items size             override fun areItemsTheSame oldItemPosition  Int  newItemPosition  Int                    viewPager adapter  getItemId oldItemPosition     viewModel items newItemPosition  id              override fun areContentsTheSame oldItemPosition  Int  newItemPosition  Int                    areItemsTheSame oldItemPosition  newItemPosition             false           dispatchUpdatesTo viewPager adapter

[android] Update ViewPager dynamically?

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