Fragments onResume from back stack

Question

I m using the compatibility package to use Fragments with Android 2 2   When using fragments  and adding transitions between them to the backstack  I d like to achieve the same behavior of onResume of an activity  i e   whenever a fragment is brought to  foreground   visible to the user  after poping out of the backstack  I d like some kind of callback to be activated within the fragment  to perform certain changes on a shared UI resource  for instance    I saw that there is no built in callback within the fragment framework  is there s a good practice in order to achieve this

User · Answer

public abstract class RootFragment extends Fragment implements OnBackPressListener      Override  public boolean onBackPressed       return new BackPressImpl this  onBackPressed         public abstract void OnRefreshUI         public class BackPressImpl implements OnBackPressListener     private Fragment parentFragment    public BackPressImpl Fragment parentFragment      this parentFragment   parentFragment        Override  public boolean onBackPressed         RootFragment  parentFragment  OnRefreshUI           and final extent your Frament from RootFragment to see effect

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onResume   for the fragment works fine     public class listBook extends Fragment        private String listbook last subtitle            Override        public void onCreate Bundle savedInstanceState             String thisFragSubtitle    String  getActivity   getActionBar   getSubtitle            listbook last subtitle   thisFragSubtitle                     Override         public void onResume                super onResume                getActivity   getActionBar   setSubtitle listbook last subtitle

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If a fragment is put on backstack  Android simply destroys its view  The fragment instance itself is not killed  A simple way to start should to to listen to the onViewCreated event  an put you  onResume    logic there   boolean fragmentAlreadyLoaded   false       Override     public void onViewCreated View view   Nullable Bundle savedInstanceState               TODO Auto-generated method stub         super onViewCreated view  savedInstanceState            if  savedInstanceState    null  amp  amp   fragmentAlreadyLoaded                fragmentAlreadyLoaded   true                  Code placed here will be executed once                      Code placed here will be executed even when the fragment comes from backstack

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A little improved and wrapped into a manager solution   Things to keep in mind  FragmentManager is not a singleton  it manages only Fragments within Activity  so in every activity it will be new  Also  this solution so far doesn t take ViewPager into account that calls setUserVisibleHint   method helping to control visiblity of Fragments   Feel free to use following classes when dealing with this issue  uses Dagger2 injection   Call in Activity     inject FragmentBackstackStateManager instance to myFragmentBackstackStateManager FragmentManager fragmentManager   getSupportFragmentManager     myFragmentBackstackStateManager apply fragmentManager     FragmentBackstackStateManager java    Singleton public class FragmentBackstackStateManager        private FragmentManager fragmentManager        Inject     public FragmentBackstackStateManager                private BackstackCallback backstackCallbackImpl   new BackstackCallback              Override         public void onFragmentPushed Fragment parentFragment                parentFragment onPause                        Override         public void onFragmentPopped Fragment parentFragment                parentFragment onResume                          public FragmentBackstackChangeListenerImpl getListener             return new FragmentBackstackChangeListenerImpl fragmentManager  backstackCallbackImpl              public void apply FragmentManager fragmentManager            this fragmentManager   fragmentManager          fragmentManager addOnBackStackChangedListener getListener               FragmentBackstackChangeListenerImpl java   public class FragmentBackstackChangeListenerImpl implements FragmentManager OnBackStackChangedListener        private int lastBackStackEntryCount   0      private final FragmentManager fragmentManager      private final BackstackCallback backstackChangeListener       public FragmentBackstackChangeListenerImpl FragmentManager fragmentManager  BackstackCallback backstackChangeListener            this fragmentManager   fragmentManager          this backstackChangeListener   backstackChangeListener          lastBackStackEntryCount   fragmentManager getBackStackEntryCount               private boolean wasPushed int backStackEntryCount            return lastBackStackEntryCount  lt  backStackEntryCount             private boolean wasPopped int backStackEntryCount            return lastBackStackEntryCount  gt  backStackEntryCount             private boolean haveFragments             List lt Fragment gt  fragmentList   fragmentManager getFragments            return fragmentList    null  amp  amp   fragmentList isEmpty                           If we push a fragment to backstack then parent would be the one before   gt  size - 2        If we pop a fragment from backstack logically it should be the last fragment in the list  but in Android popping a fragment just makes list entry null keeping list size intact  thus it s also size - 2                return fragment that is parent to the one that is pushed to or popped from back stack             private Fragment getParentFragment             List lt Fragment gt  fragmentList   fragmentManager getFragments            return fragmentList get Math max 0  fragmentList size   - 2                Override     public void onBackStackChanged             int currentBackStackEntryCount   fragmentManager getBackStackEntryCount            if  haveFragments                  Fragment parentFragment   getParentFragment                   will be null if was just popped and was last in the stack             if  parentFragment    null                    if  wasPushed currentBackStackEntryCount                         backstackChangeListener onFragmentPushed parentFragment                     else if  wasPopped currentBackStackEntryCount                         backstackChangeListener onFragmentPopped parentFragment                                                      lastBackStackEntryCount   currentBackStackEntryCount            BackstackCallback java   public interface BackstackCallback       void onFragmentPushed Fragment parentFragment        void onFragmentPopped Fragment parentFragment

User · Answer

I ve changed the suggested solution a little bit  Works better for me like that   private OnBackStackChangedListener getListener         OnBackStackChangedListener result   new OnBackStackChangedListener             public void onBackStackChanged                 FragmentManager manager   getSupportFragmentManager                if  manager    null                    int backStackEntryCount   manager getBackStackEntryCount                    if  backStackEntryCount    0                        finish                                      Fragment fragment   manager getFragments                                               get backStackEntryCount - 1                   fragment onResume                                       return result

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In my activity onCreate    getSupportFragmentManager   addOnBackStackChangedListener getListener       Use this method to catch specific Fragment and call onResume    private FragmentManager OnBackStackChangedListener getListener                 FragmentManager OnBackStackChangedListener result   new FragmentManager OnBackStackChangedListener                         public void onBackStackChanged                                 Fragment currentFragment   getSupportFragmentManager   findFragmentById R id fragment container                   if  currentFragment instanceof YOURFRAGMENT                        currentFragment onResume                                                        return result

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I have used enum FragmentTags to define all my fragment classes   TAG FOR FRAGMENT A A class   TAG FOR FRAGMENT B B class   TAG FOR FRAGMENT C C class    pass FragmentTags TAG FOR FRAGMENT A name   as fragment tag   and now on    Override public void onBackPressed       FragmentManager fragmentManager   getFragmentManager       Fragment current      fragmentManager findFragmentById R id fragment container       FragmentTags fragmentTag   FragmentTags valueOf current getTag        switch fragmentTag       case TAG FOR FRAGMENT A          finish            break     case TAG FOR FRAGMENT B          fragmentManager popBackStack            break     case default      break

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After a popStackBack   you can use the following callback   onHiddenChanged boolean hidden  within your fragment

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The following section at Android Developers describes a communication mechanism Creating event callbacks to the activity  To quote a line from it      A good way to do that is to define a callback interface inside the fragment and require that the host activity implement it  When the activity receives a callback through the interface  it can share the information with other fragments in the layout as necessary    Edit   The fragment has an onStart      which is invoked when the fragment is visible to the user  Similarly an onResume      when visible and actively running  These are tied to their activity counterparts  In short  use onResume

User · Answer

This is the correct answer you can call onResume   providing the fragment is attached to the activity  Alternatively you can use onAttach and onDetach

User · Answer

For a lack of a better solution  I got this working for me  Assume I have 1 activity  MyActivity  and few fragments that replaces each other  only one is visible at a time    In MyActivity  add this listener   getSupportFragmentManager   addOnBackStackChangedListener getListener        As you can see I m using the compatibility package    getListener implementation   private OnBackStackChangedListener getListener                 OnBackStackChangedListener result   new OnBackStackChangedListener                         public void onBackStackChanged                                                     FragmentManager manager   getSupportFragmentManager                     if  manager    null                                        MyFragment currFrag    MyFragment  manager findFragmentById R id fragmentItem                        currFrag onFragmentResume                                                                           return result          MyFragment onFragmentResume   will be called after a  Back  is pressed  few caveats though    It assumes you added all transactions to the backstack  using FragmentTransaction addToBackStack    It will be activated upon each stack change  you can store other stuff in the back stack such as animation  so you might get multiple calls for the same instance of fragment

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My workaround is to get the current title of the actionbar in the Fragment before setting it to the new title  This way  once the Fragment is popped  I can change back to that title    Override public void onResume         super onResume           Get Backup current title     mTitle     ActionBarActivity  getActivity    getSupportActionBar                getTitle           Set new title       ActionBarActivity  getActivity    getSupportActionBar            setTitle R string this fragment title       Override public void onDestroy            Set title back       ActionBarActivity  getActivity    getSupportActionBar            setTitle mTitle        super onDestroy

[android] Fragments onResume from back stack

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