Android tabs fragment crashes when changing to landscape -

i have activity 3 tabs using fragments, works fine when working in portrait mode, however, when change landscape, crashes. code:

public class mainmenuactivity extends activity {      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main_menu);          actionbar actionbar = getactionbar();         actionbar.setnavigationmode(actionbar.navigation_mode_tabs);          string label1 = getresources().getstring(r.string.usermaintab);         tab tab = actionbar.newtab();         tab.settext(label1);         tablistener<usertabactivity> tl = new tablistener<usertabactivity>(this, label1, usertabactivity.class);         tab.settablistener(tl);         actionbar.addtab(tab);          string label2 = getresources().getstring(r.string.credentialgroupmaintab);         tab tab2 = actionbar.newtab();         tab2.settext(label2);         tablistener<credentialgroupactivity> tl2 = new tablistener<credentialgroupactivity>(this, label2, credentialgroupactivity.class);         tab2.settablistener(tl2);         actionbar.addtab(tab2);          string label3 = getresources().getstring(r.string.credentialtabheader);         tab tab3 = actionbar.newtab();         tab3.settext(label3);         tablistener<credentialtabactivity> tl3 = new tablistener<credentialtabactivity>(this, label2, credentialtabactivity.class);         tab3.settablistener(tl3);         actionbar.addtab(tab3);           }      @override     public boolean oncreateoptionsmenu(menu menu) {         // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.main_menu, menu);         return true;     }         public static class tablistener<t extends fragment> implements actionbar.tablistener{          private fragment mfragment;         private final activity mactivity;         private final string mtag;         private final class<t> mclass;          public tablistener(activity activity, string tag, class<t> clz){             mactivity = activity;             mtag = tag;             mclass = clz;              mfragment = mactivity.getfragmentmanager().findfragmentbytag(mtag);             if(mfragment != null && !mfragment.isdetached()){                 fragmenttransaction ft = mactivity.getfragmentmanager().begintransaction();                 ft.detach(mfragment);                 ft.commit();             }         }          @override         public void ontabreselected(tab arg0, fragmenttransaction arg1) {             // todo auto-generated method stub         }          @override         public void ontabselected(tab arg0, fragmenttransaction arg1) {             // todo auto-generated method stub             if(mfragment == null){                 mfragment = fragment.instantiate(mactivity, mclass.getname());                 arg1.add(android.r.id.content, mfragment, mtag);             } else{                 arg1.attach(mfragment);             }         }          @override         public void ontabunselected(tab arg0, fragmenttransaction arg1) {             // todo auto-generated method stub             if(mfragment != null){                 arg1.detach(mfragment);             }         }      }  } 

could tell me why not working? error is:

java.lang.runtimeexception: unable destroy activity{activity_name} : java.lang.nullpointerexception 

i have noticed fails until click on of tabs, , try change landscape, haven't been able identify in code what's happening, , also, when change view, loses tab positioned.

thanks in advanced!

edit

in order keep selected tab after changing orientation, ended doing this, suggestions made nathaniel waggoner , karthikk:

protected void onsaveinstancestate(bundle outstate) {     // todo auto-generated method stub     super.onsaveinstancestate(outstate);      outstate.putint("tabstate", actionbar.getselectedtab().getposition()); }  //in oncreate method     if(savedinstancestate != null ){         actionbar.selecttab(actionbar.gettabat(savedinstancestate.getint("tabstate")));     } 

thanks!!

are overriding ondestroy in fragments? npe show symptom i've seen when i've overidden ondestroy in fragments used in tabs. remove override if , see if clears issue.