android - Nested fragments created twice on orientation change -

i created example understand lifecycle of android fragments @ screen orientation change.

mainactivity container drawerlayout, drawerlayout allows choose fragment, fill mainactivity screen.

public class mainactivity extends actionbaractivity { ... @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);      log.d("mainactivity", "oncreate savedinstancestate = "+(savedinstancestate == null ? "null" : "not null"));  ...     mdrawerlist.setonitemclicklistener(new adapterview.onitemclicklistener() {          @override         public void onitemclick(adapterview<?> parent, view view, int position, long id) {      if (position == 0) {             if (viewingposition == position) {                 mdrawerlayout.closedrawer(mdrawerlist);                 return;             }             getsupportfragmentmanager()                     .begintransaction()                     .replace(r.id.contentframe, new parentpagerfragment(),                                 parentpagerfragment.tag).commit();            viewingposition = 0;      }      if (position == 1) {             if (viewingposition == position) {                 mdrawerlayout.closedrawer(mdrawerlist);                 return;             }             getsupportfragmentmanager().begintransaction()                 .replace(r.id.contentframe, childtextviewfragment.newinstance("hello fragment"), childtextviewfragment.tag)                 .commit();             viewingposition = 1;     } } ...  getsupportfragmentmanager()             .begintransaction()             .replace(r.id.contentframe, new parentpagerfragment(),                     parentpagerfragment.tag).commit(); ... 

then have parentpagerfragment, parentpagerfragment contains viewpager 3 childtextviewfragments.

public class parentpagerfragment extends fragment { ...  @override public view oncreateview(layoutinflater inflater, viewgroup container, bundle savedinstancestate) {     log.d(tag, "oncreateview savedinstancestate "+(savedinstancestate == null ? "null" : "not null"));      view v = inflater.inflate(r.layout.fragment_pager, container, false);      list<childtextviewfragment> viewfragments = new arraylist<>();     viewfragments.add(childtextviewfragment.newinstance("fragment1"));     viewfragments.add(childtextviewfragment.newinstance("fragment2"));     viewfragments.add(childtextviewfragment.newinstance("fragment3"));      mypageradapter mpageradapter = new mypageradapter(getchildfragmentmanager(), viewfragments);      viewpager mviewpager = (viewpager) v.findviewbyid(r.id.pager);     mviewpager.setadapter(mpageradapter);      return v; }  ... }   class mypageradapter extends fragmentpageradapter {      list<childtextviewfragment> viewfragments;      public mypageradapter(fragmentmanager fm, list<childtextviewfragment> viewfragments) {         super(fm);         this.viewfragments = viewfragments;     }      @override     public fragment getitem(int index) {         return viewfragments.get(index);      }      @override     public int getcount() {         return viewfragments.size();     }      @override     public charsequence getpagetitle(int position){         if(position == 0) {             return "fragment1";         } else if (position == 1) {             return "fragment2";         } else {             return "fragment3";         }     }  } 

childtextviewfragment used display text

public class childtextviewfragment extends fragment { ...  @override public view oncreateview(layoutinflater inflater, viewgroup container, bundle savedinstancestate) {      view view = inflater.inflate(r.layout.fragment_text, container, false);      textview mtextview = (textview) view.findviewbyid(r.id.textview1);     string text = getarguments().getstring(text_key);     mtextview.settext(text);      log.d(tag, text+" :: oncreateview savedinstancestate " + (savedinstancestate == null ? "null" : "not null"));      return view;  } 

after run example first time got these logs messages expected:

06-01 10:34:24.154: d/mainactivity(8426): oncreate savedinstancestate = null 06-01 10:34:24.272: d/parentpagerfragment(8426): oncreateview savedinstancestate null 06-01 10:34:24.389: d/childtextviewfragment(8426): fragment1 :: oncreateview savedinstancestate null 06-01 10:34:24.390: d/childtextviewfragment(8426): fragment2 :: oncreateview savedinstancestate null 

the surprise appeared, when rotated display:

06-01 10:36:15.697: d/mainactivity(8426): oncreate savedinstancestate = not null 06-01 10:36:15.713: d/parentpagerfragment(8426): oncreateview savedinstancestate not null 06-01 10:36:15.716: d/childtextviewfragment(8426): fragment1 :: oncreateview savedinstancestate not null 06-01 10:36:15.717: d/childtextviewfragment(8426): fragment2 :: oncreateview savedinstancestate not null  06-01 10:36:15.718: d/parentpagerfragment(8426): oncreateview savedinstancestate null 06-01 10:36:15.739: d/childtextviewfragment(8426): fragment1 :: oncreateview savedinstancestate null 06-01 10:36:15.740: d/childtextviewfragment(8426): fragment2 :: oncreateview savedinstancestate null 

i expecting fragments restored , displayed again (like first 4 line of logs shows), don't understand, why fragments created again savedinstancestate = null ? common behavior, or doing wrong ?

try adding null check savedinstancestate in mainactivity oncreate(bundle savedinstancestate) method this

        if (savedinstancestate == null) {              getsupportfragmentmanager()             .begintransaction()             .replace(r.id.contentframe, new parentpagerfragment(),                     parentpagerfragment.tag).commit();         }