I have a button that adds the ParentFragment. Inside theres a Viewpager containing two ListFragments. The first time adding the ParentFragment, everything works fine, except when I press back and add the ParentFragment again. The ParentFragment gets created as usual but when it tries to create the Viewpager it somehow crashes the application.
ParentFragment
|
V
ListFragment 1 <-- Viewpager --> ListFragment 2
Error log:
FATAL EXCEPTION: main
Process: at.umoser.fab.musikbox, PID: 16900
java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:667)
at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:211)
at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1319)
at android.view.View.dispatchRestoreInstanceState(View.java:13639)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2889)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2895)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2895)
at android.view.View.restoreHierarchyState(View.java:13617)
at android.support.v4.app.Fragment.restoreViewState(Fragment.java:468)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1094)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5312)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
This is how I call the Viewpager using getChildFragmentManager() in the 'ParentFragment**:
mPager = (ViewPager) rootView.findViewById(R.id.pager);
mPagerAdapter = new ScreenSlidePagerAdapter(getChildFragmentManager(), connection);
mPager.setAdapter(mPagerAdapter);
Apparently using getChildFragmentManager() instead of using getFragmentManager() is the right way for nested fragments, although the app doesn't crash when using getFragmentManager(), the viewpager simply doesn't appear at all.
Does the Viewpager or its Adapter call the onRestoreInstanceState/restoreState Methods (check Error Log) everytime its created, or does this happen only in the second time the ParentFragment is added?
If so, how can I force it to create everything from scratch instead of restoring the state? Or is there another solution.
