android - FragmentStatePageAdapter doesn't remove child fragments -

having problem fragmentstatepageradapter , screen change orientation (saving state guess). layout of app following:

activity -->          fragment          fragment b (contains fragmentstatepageradapter) wich shows 2 fragments                    -->                      fragment b1                      fragment b2 

all fragments mentioned inherit basefragment class doesn't special keeping "global" vars need. when activity starts loads fragment a. menu replace fragment a fragment b. fragment b source following:

public class fragment b extends basefragment {      public static string tag = "b_fragment";     private mycustompageradapter adapter;     private arraylist<string> tags = new arraylist<>();     private viewpager mviewpager;      @override     public void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         adapter = new mycustompageradapter(getfragmentmanager());         //adapter = new mycustompageradapter(getchildfragmentmanager());         tags.add(fragmentb1.tag);         tags.add(fragmentb2.tag);     }      @override     public view oncreateview(layoutinflater inflater, viewgroup container,                          bundle savedinstancestate) {         return inflater.inflate(r.layout.fragment_sample, container, false);     }      @override     public void onviewcreated(view view, bundle savedinstancestate) {         super.onviewcreated(view, savedinstancestate);          mviewpager = (viewpager) view.findviewbyid(r.id.viewpager);         mviewpager.setadapter(adapter);         slidingtablayout mslidingtablayout = (slidingtablayout)view.findviewbyid(r.id.sliding_tabs);         mslidingtablayout.setviewpager(mviewpager);             }      class mycustompageradapter extends fragmentstatepageradapter {     //class mycustompageradapter extends fragmentpageradapter {          fragmentmanager mgr;         public sparsearray<fragment> registeredfragments = new sparsearray<fragment>();          public prepagatepageradapter(fragmentmanager mgr) {             super(mgr);             this.mgr = mgr;         }          @override         public int getcount() {             return 2;         }          @override         public fragment getitem(int position) {             switch (position) {                 case 0:                     return new fragmentb1();                 case 1:                     return new fragmentb2();             }             return null;         }          @override         public object instantiateitem(viewgroup container, int position)  {             fragment fragment = (fragment)  super.instantiateitem(container, position);             registeredfragments.put(position, fragment);             return fragment;         }          @override         public void destroyitem(viewgroup container, int position, object object) {             registeredfragments.remove(position);             super.destroyitem(container, position, object);         }          public fragment getregisteredfragment(int position) {             return registeredfragments.get(position);         }     } } 

the problem happens when go fragment b go again fragment a , change orientation: see while debugging on onattach() method of fragment a in fragmentmanager fragment b no more present (replaced fragment a) fragment b1 , b2 there , called rispective onattach() methods, resulting in weird behaviours of layout. didn't child fragments should remove fragmentmanager?

at moment don't know if more details needed. can give further if need.