FragmentStatePagerAdapter with ChildFragmentManager - FragmentManagerImpl.getFragment results in NullPointerException

Question

EDIT 2

I now managed to get rid of the error with using the trick from here https://code.google.com/p/android/issues/detail?id=42601#c10 so that's the reoson why my last edit is placed on top of my question.

But this led to the next error:

java.lang.NullPointerException at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:569) at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:211) at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1281) at android.view.View.dispatchRestoreInstanceState(View.java:12043) at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2688) at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2694) at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2694) at android.view.View.restoreHierarchyState(View.java:12021) at android.support.v4.app.Fragment.restoreViewState(Fragment.java:425) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:949) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104) at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460) at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440) at android.os.Handler.handleCallback(Handler.java:615) at android.os.Handler.dispatchMessage(Handler.java:92) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4800) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:798) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:565) at dalvik.system.NativeStart.main(Native Method) 

And now I don't know where to continue...

Edit 0 - FIRST question

I get following exception:

java.lang.IllegalStateException: No activity at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1091) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086) at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1877) at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1492) at android.support.v4.app._HoloFragment.performActivityCreated(_HoloFragment.java:251) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104) at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460) at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440) at android.os.Handler.handleCallback(Handler.java:615) at android.os.Handler.dispatchMessage(Handler.java:92) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4800) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:798) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:565) at dalvik.system.NativeStart.main(Native Method) 

I have no idea where to start. I'm using the up to date support library (v4, rev18).

Everything works fine until I add a Fragment which holds a ViewPager in combination with FragmentStatePagerAdapter.

I'm using the support library everywhere, I tried the solutions from https://code.google.com/p/android/issues/detail?id=42601...

But nothing worked yet...

I don't know where to start, does anyone have a hint?

EDIT 1: BACKGROUND and Code

1) In my MainActivity I use following:

The third page has the viewpager...

public void setPage(int pos, boolean addToBackStack)  {     Fragment nextFragment = null;     FragmentTransaction transaction = null;      switch (pos)     {         case 0:             if (mFragmentAllRoutines == null)                 mFragmentAllRoutines = new RoutinesListFragment();             if (!mFragmentAllRoutines.isVisible())                 nextFragment = mFragmentAllRoutines;             break;         case 1:             if (mFragmentRoutine == null)                 mFragmentRoutine = new RoutineFragment();             if (!mFragmentRoutine.isVisible())                 nextFragment = mFragmentRoutine;             break;         case 2:             if (mFragmentDay == null)                 mFragmentDay = new RoutineDayFragment();             if (!mFragmentDay.isVisible())                 nextFragment = mFragmentDay;             break;         default:             break;     }      if (nextFragment != null)     {         // Fragment prevFragment = getSupportFragmentManager().findFragmentById(R.id.fragment);         transaction = getSupportFragmentManager().beginTransaction();         // if (prevFragment != null)         //    transaction.detach(prevFragment);         transaction.replace(R.id.fragment, nextFragment, nextFragment.getClass().getName());         // transaction.attach(nextFragment);         if (addToBackStack)             transaction.addToBackStack(null);         transaction.commit();     } } 

2) the third fragment:

It's a simple Fragment with a ViewPager and a FragmentStatePagerAdapter. The FragmentStatePagerAdapter get's the getChildFragmentManager() as FragmentManager. And somewhere there seems to be the problem.

Answer 1

I would need to see more code in order to know where to apply this ... but I had a similar situation as you did... I solved the ChildFragmentManager issue the same way, and got the same NullPointerException, as you have.

I did manage to solve it... I'll try to describe my solution, as with the code you supplied I am unsure as to where to apply the "fix" ... It really is a fix ... it's not an elegant way to solve this! It did however helped me, and I don't need to restore states once I navigate away on the view Pager, so no downside for me.

I have multiple Fragments, that implement the static bit of code and the onDetach (on https://code.google.com/p/android/issues/detail?id=42601#c10), each fragment has a pager, and onCreateView I attach an adapter that extends FragmentStatePagerAdapter.

on those adapters I have overridden the restoreState method to do nothing

    @Override public void restoreState(Parcelable arg0, ClassLoader arg1) {     //do nothing here! no call to super.restoreState(arg0, arg1); } 

Again, this is not the best way... but it did solve my problem.

Best of luck!