I have an Activity with a FragmentStatePagerAdapter, but I have to use NavigationView, so I have to move the Activities into fragments to be able to display them contents in the same Activity to be able to navigate between them by the NavigationView.
At first when I returned to the Fragment that contains the FragmentStatePagerAdapter, the Fragments in the adapter weren't displayed. I read some SO posts, and finally I found out I have to pass ChildFragmentManager instead of SupportFragmentManager to FragmentStatePagerAdapter since it contained by a Fragment instead of an Activity.
But in this case I get this error, and I can't find out what goes wrong. If I use FragmentPagerAdapter instead of FragmentStatePagerAdapter it works, but I'd like to use FragmentStatePagerAdapter.
I got this error:
10-12 12:36:30.022 25801-25801/com.aff.index.main.debug E/AndroidRuntime: FATAL EXCEPTION: main Process: com.aff.index.main.debug, PID: 25801 java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.util.SparseArray.get(int)' on a null object reference at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:902) at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:216) at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1453) at android.view.View.dispatchRestoreInstanceState(View.java:15751) at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3231) at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3237) at android.view.View.restoreHierarchyState(View.java:15729) at android.support.v4.app.Fragment.restoreViewState(Fragment.java:510) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1445) at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1740) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1809) at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:799) at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2580) at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2367) at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2322) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2229) at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:700) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
