Fragment onCreateView and onActivityCreated called twice

Question

I m developing an app using Android 4 0 ICS and fragments   Consider this modified example from the ICS 4 0 3  API level 15  API s demo example app   public class FragmentTabs extends Activity    private static final String TAG   FragmentTabs class getSimpleName      Override protected void onCreate Bundle savedInstanceState        super onCreate savedInstanceState        final ActionBar bar   getActionBar        bar setNavigationMode ActionBar NAVIGATION MODE TABS       bar setDisplayOptions 0  ActionBar DISPLAY SHOW TITLE        bar addTab bar newTab                setText  Simple                setTabListener new TabListener lt SimpleFragment gt                       this   mysimple   SimpleFragment class          if  savedInstanceState    null            bar setSelectedNavigationItem savedInstanceState getInt  tab   0            Log d TAG   FragmentTabs onCreate tab      savedInstanceState getInt  tab             Log d TAG   FragmentTabs onCreate number      savedInstanceState getInt  number                Override protected void onSaveInstanceState Bundle outState        super onSaveInstanceState outState       outState putInt  tab   getActionBar   getSelectedNavigationIndex        public static class TabListener lt T extends Fragment gt  implements ActionBar TabListener       private final Activity mActivity      private final String mTag      private final Class lt T gt  mClass      private final Bundle mArgs      private Fragment mFragment       public TabListener Activity activity  String tag  Class lt T gt  clz            this activity  tag  clz  null              public TabListener Activity activity  String tag  Class lt T gt  clz  Bundle args            mActivity   activity          mTag   tag          mClass   clz          mArgs   args              Check to see if we already have a fragment for this tab  probably            from a previously saved state   If so  deactivate it  because our            initial state is that a tab isn t shown          mFragment   mActivity getFragmentManager   findFragmentByTag mTag           if  mFragment    null  amp  amp   mFragment isDetached                  Log d TAG   constructor  detaching fragment     mTag               FragmentTransaction ft   mActivity getFragmentManager   beginTransaction                ft detach mFragment               ft commit                         public void onTabSelected Tab tab  FragmentTransaction ft            if  mFragment    null                mFragment   Fragment instantiate mActivity  mClass getName    mArgs               Log d TAG   onTabSelected adding fragment     mTag               ft add android R id content  mFragment  mTag             else               Log d TAG   onTabSelected attaching fragment     mTag               ft attach mFragment                        public void onTabUnselected Tab tab  FragmentTransaction ft            if  mFragment    null                Log d TAG   onTabUnselected detaching fragment     mTag               ft detach mFragment                        public void onTabReselected Tab tab  FragmentTransaction ft            Toast makeText mActivity   Reselected    Toast LENGTH SHORT  show             public static class SimpleFragment extends Fragment       TextView textView      int mNum                  When creating  retrieve this instance s number from its arguments               Override     public void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           Log d FragmentTabs TAG   onCreate      savedInstanceState    null     state     savedInstanceState getInt  number       no state             if savedInstanceState    null                mNum   savedInstanceState getInt  number              else               mNum   25                        Override     public void onActivityCreated Bundle savedInstanceState            Log d TAG   onActivityCreated            if savedInstanceState    null                Log d TAG   saved variable number      savedInstanceState getInt  number                       super onActivityCreated savedInstanceState               Override     public void onSaveInstanceState Bundle outState            Log d TAG   onSaveInstanceState saving      mNum           outState putInt  number   mNum           super onSaveInstanceState outState               Override     public View onCreateView LayoutInflater inflater  ViewGroup container  Bundle savedInstanceState            Log d FragmentTabs TAG   onCreateView      savedInstanceState    null     state      savedInstanceState getInt  number       no state             textView   new TextView getActivity             textView setText  Hello world      mNum           textView setBackgroundDrawable getResources   getDrawable android R drawable gallery thumb            return textView               Here is the output retrieved from running this example and then rotating the phone   06-11 11 31 42 559  D FragmentTabs 10726   onTabSelected adding fragment mysimple 06-11 11 31 42 559  D FragmentTabs 10726   onCreate no state 06-11 11 31 42 559  D FragmentTabs 10726   onCreateView no state 06-11 11 31 42 567  D FragmentTabs 10726   onActivityCreated 06-11 11 31 45 286  D FragmentTabs 10726   onSaveInstanceState saving  25 06-11 11 31 45 325  D FragmentTabs 10726   onCreate state 25 06-11 11 31 45 340  D FragmentTabs 10726   constructor  detaching fragment mysimple 06-11 11 31 45 340  D FragmentTabs 10726   onTabSelected attaching fragment mysimple 06-11 11 31 45 348  D FragmentTabs 10726   FragmentTabs onCreate tab  0 06-11 11 31 45 348  D FragmentTabs 10726   FragmentTabs onCreate number  0 06-11 11 31 45 348  D FragmentTabs 10726   onCreateView state  25 06-11 11 31 45 348  D FragmentTabs 10726   onActivityCreated 06-11 11 31 45 348  D FragmentTabs 10726   saved variable number  25 06-11 11 31 45 348  D FragmentTabs 10726   onCreateView no state 06-11 11 31 45 348  D FragmentTabs 10726   onActivityCreated   My question is  why is the onCreateView and onActivityCreated called twice  The first time with a Bundle with the saved state and the second time with a null savedInstanceState    This is causing problems with retaining the state of the fragment on rotation

User · Answer

I was scratching my head about this for a while too, and since Dave's explanation is a little hard to understand I'll post my (apparently working) code:

private class TabListener<T extends Fragment> implements ActionBar.TabListener {
    private Fragment mFragment;
    private Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;

    public TabListener(Activity activity, String tag, Class<T> clz) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
        mFragment=mActivity.getFragmentManager().findFragmentByTag(mTag);
    }

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        if (mFragment == null) {
            mFragment = Fragment.instantiate(mActivity, mClass.getName());
            ft.replace(android.R.id.content, mFragment, mTag);
        } else {
            if (mFragment.isDetached()) {
                ft.attach(mFragment);
            }
        }
    }

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {
            ft.detach(mFragment);
        }
    }

    public void onTabReselected(Tab tab, FragmentTransaction ft) {
    }
}

As you can see it's pretty much like the Android sample, apart from not detaching in the constructor, and using replace instead of add.

After much headscratching and trial-and-error I found that finding the fragment in the constructor seems to make the double onCreateView problem magically go away (I assume it just ends up being null for onTabSelected when called through the ActionBar.setSelectedNavigationItem() path when saving/restoring state).

User · Answer

It looks to me like it s because you are instantiating your TabListener every time    so the system is recreating your fragment from the savedInstanceState and then you are doing it again in your onCreate   You should wrap that in a if savedInstanceState    null  so it only fires if there is no savedInstanceState

User · Answer

I have had the same problem with a simple Activity carrying only one fragment  which would get replaced sometimes   I then realized I use onSaveInstanceState only in the fragment  and onCreateView to check for savedInstanceState   not in the activity   On device turn the activity containing the fragments gets restarted and onCreated is called  There I did attach the required fragment  which is correct on the first start    On the device turn Android first re-created the fragment that was visible and then called onCreate of the containing activity where my fragment was attached  thus replacing the original visible one   To avoid that I simply changed my activity to check for savedInstanceState   protected void onCreate Bundle savedInstanceState        super onCreate savedInstanceState    if  savedInstanceState    null       making sure you are not attaching the fragments again as they have   been    already added       return       else       following code to attach fragment initially          I did not even Overwrite onSaveInstanceState of the activity

User · Answer

The two upvoted answers here show solutions for an Activity with navigation mode NAVIGATION MODE TABS  but I had the same issue with a NAVIGATION MODE LIST  It caused my Fragments to inexplicably lose their state when the screen orientation changed  which was really annoying  Thankfully  due to their helpful code I managed to figure it out   Basically  when using a list navigation    onNavigationItemSelected  is automatically called when your activity is created re-created  whether you like it or not  To prevent your Fragment sonCreateView  from being called twice  this initial automatic call toonNavigationItemSelected  should check whether the Fragment is already in existence inside your Activity  If it is  return immediately  because there is nothing to do  if it isn t  then simply construct the Fragment and add it to the Activity like you normally would  Performing this check prevents your Fragment from needlessly being created again  which is what causesonCreateView    to be called twice   See my onNavigationItemSelected   implementation below   public class MyActivity extends FragmentActivity implements ActionBar OnNavigationListener       private static final String STATE SELECTED NAVIGATION ITEM    selected navigation item        private boolean mIsUserInitiatedNavItemSelection              constructor code  etc        Override     public void onRestoreInstanceState Bundle savedInstanceState                super onRestoreInstanceState savedInstanceState            if  savedInstanceState containsKey STATE SELECTED NAVIGATION ITEM                         getActionBar   setSelectedNavigationItem savedInstanceState getInt STATE SELECTED NAVIGATION ITEM                          Override     public void onSaveInstanceState Bundle outState                outState putInt STATE SELECTED NAVIGATION ITEM  getActionBar   getSelectedNavigationIndex              super onSaveInstanceState outState               Override     public boolean onNavigationItemSelected int position  long id                    Fragment fragment          switch  position                               choose and construct fragment here                       is this the automatic  non-user initiated  call to onNavigationItemSelected              that occurs when the activity is created re-created          if   mIsUserInitiatedNavItemSelection                           all subsequent calls to onNavigationItemSelected   won t be automatic             mIsUserInitiatedNavItemSelection   true                  has the same fragment already replaced the container and assumed its id              Fragment existingFragment   getSupportFragmentManager   findFragmentById R id container               if  existingFragment    null  amp  amp  existingFragment getClass   equals fragment getClass                                   return true    nothing to do  because the fragment is already there                                   getSupportFragmentManager   beginTransaction   replace R id container  fragment  commit            return true            I borrowed inspiration for this solution from here

User · Answer

Ok  Here s what I found out    What I didn t understand is that all fragments that are attached to an activity when a config change happens  phone rotates  are recreated and added back to the activity   which makes sense   What was happening in the TabListener constructor was the tab was detached if it was found and attached to the activity  See below   mFragment   mActivity getFragmentManager   findFragmentByTag mTag       if  mFragment    null  amp  amp   mFragment isDetached              Log d TAG   constructor  detaching fragment     mTag           FragmentTransaction ft   mActivity getFragmentManager   beginTransaction            ft detach mFragment           ft commit            Later in the activity onCreate the previously selected tab was selected from the saved instance state  See below   if  savedInstanceState    null        bar setSelectedNavigationItem savedInstanceState getInt  tab   0        Log d TAG   FragmentTabs onCreate tab      savedInstanceState getInt  tab         Log d TAG   FragmentTabs onCreate number      savedInstanceState getInt  number         When the tab was selected it would be reattached in the onTabSelected callback    public void onTabSelected Tab tab  FragmentTransaction ft        if  mFragment    null            mFragment   Fragment instantiate mActivity  mClass getName    mArgs           Log d TAG   onTabSelected adding fragment     mTag           ft add android R id content  mFragment  mTag         else           Log d TAG   onTabSelected attaching fragment     mTag           ft attach mFragment             The fragment being attached is the second call to the onCreateView and onActivityCreated methods   The first being when the system is recreating the acitivity and all attached fragments  The first time the onSavedInstanceState Bundle would have saved data but not the second time    The solution is to not detach the fragment in the TabListener constructor   just leave it attached   You still need to find it in the FragmentManager by it s tag  Also  in the onTabSelected method I check to see if the fragment is detached before I attach it  Something like this   public void onTabSelected Tab tab  FragmentTransaction ft                if  mFragment    null                    mFragment   Fragment instantiate mActivity  mClass getName    mArgs                   Log d TAG   onTabSelected adding fragment     mTag                   ft add android R id content  mFragment  mTag                 else                    if mFragment isDetached                          Log d TAG   onTabSelected attaching fragment     mTag                       ft attach mFragment                     else                       Log d TAG   onTabSelected fragment already attached     mTag

[android] Fragment onCreateView and onActivityCreated called twice

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