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<SimpleFragment>(                     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<T extends Fragment> implements ActionBar.TabListener {     private final Activity mActivity;     private final String mTag;     private final Class<T> mClass;     private final Bundle mArgs;     private Fragment mFragment;      public TabListener(Activity activity, String tag, Class<T> clz) {         this(activity, tag, clz, null);     }      public TabListener(Activity activity, String tag, Class<T> 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 && !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.

Answer 1

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).

Answer 2

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.