Android Fragment lifecycle makes app crash -

when fragment displaying info custom session object created, need load ui properties selected session.

this works fine when fragment created first time wrote code set in onstart, because layout isn't inflated until oncreateview, called before onstart. (http://developer.android.com/guide/components/fragments.html)

the problem : whenever phone rotated, app crashes, apparently because onstart gets called,

i tried using onactivitycreated , onresume instead neither worked, , 3 functions called automatically after oncreateview

what can without disabling rotation ?

there diagram of fragment lifecycle here: http://developer.android.com/guide/components/fragments.html

05-12 01:03:12.968  21599-21599/com.example.kn.ib w/dalvikvm﹕ threadid=1: thread exiting uncaught exception (group=0x418f3da0)     05-12 01:03:12.968  21599-21599/com.example.kn.ib e/androidruntime﹕ fatal exception: main         process: com.example.kn.ib, pid: 21599         java.lang.runtimeexception: unable start activity componentinfo{com.example.kn.ib/com.example.kn.ib.ibcentralactivity}: java.lang.nullpointerexception                 @ android.app.activitythread.performlaunchactivity(activitythread.java:2305)                 @ android.app.activitythread.handlelaunchactivity(activitythread.java:2363)                 @ android.app.activitythread.handlerelaunchactivity(activitythread.java:3924)                 @ android.app.activitythread.access$1000(activitythread.java:161)                 @ android.app.activitythread$h.handlemessage(activitythread.java:1271)                 @ android.os.handler.dispatchmessage(handler.java:102)                 @ android.os.looper.loop(looper.java:157)                 @ android.app.activitythread.main(activitythread.java:5356)                 @ java.lang.reflect.method.invokenative(native method)                 @ java.lang.reflect.method.invoke(method.java:515)                 @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:1265)                 @ com.android.internal.os.zygoteinit.main(zygoteinit.java:1081)                 @ dalvik.system.nativestart.main(native method)          caused by: java.lang.nullpointerexception                 @ com.example.karimnseir.instabeat.ibsessioninfofragment.onactivitycreated(ibsessioninfofragment.java:117)                 @ android.app.fragment.performactivitycreated(fragment.java:1708)                 @ android.app.fragmentmanagerimpl.movetostate(fragmentmanager.java:908)                 @ android.app.fragmentmanagerimpl.movetostate(fragmentmanager.java:1062)                 @ android.app.fragmentmanagerimpl.movetostate(fragmentmanager.java:1044)                 @ android.app.fragmentmanagerimpl.dispatchactivitycreated(fragmentmanager.java:1853)                 @ android.app.activity.performcreate(activity.java:5429)                 @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1105)                 @ android.app.activitythread.performlaunchactivity(activitythread.java:2269)                 at android.app.activitythread.handlelaunchactivity(activitythread.java:2363)                 at android.app.activitythread.handlerelaunchactivity(activitythread.java:3924)                 at android.app.activitythread.access$1000(activitythread.java:161)                 at android.app.activitythread$h.handlemessage(activitythread.java:1271)                 at android.os.handler.dispatchmessage(handler.java:102)                 at android.os.looper.loop(looper.java:157)                 at android.app.activitythread.main(activitythread.java:5356)                 at java.lang.reflect.method.invokenative(native method)                 at java.lang.reflect.method.invoke(method.java:515)                 at com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:1265)                 at com.android.internal.os.zygoteinit.main(zygoteinit.java:1081)                 at dalvik.system.nativestart.main(native method) 

fragment onstart (line 117 "id: "+ session._id + "\n" +)

   @override     public void onstart() {         super.onstart();           sessionid = activitycallback.getselectedsessionid();         db = activitycallback.getsessiondatabase();         instabeattimeservice = new instabeatdateandtime();          session = db.getsession(sessionid);          textview textviewfortesting = (textview) getview().findviewbyid(r.id.test);         string testtext = "\n" +                 "id: "+ session._id + "\n" +                 "lap count: "+ session._lapcount + "\n" +                 "date: "+ session._date + "\n" +                 "calories: "+ session._calories + "\n" +                 "isopen: "+ session._isopen + "\n" +                 "lastmod: "+ session._lastmod;          textviewfortesting.settext(testtext);          button savebutton = (button) getview().findviewbyid(r.id.sessioninfo_savebutton);         savebutton.setonclicklistener(this);          isopentextfield = (edittext) getview().findviewbyid(r.id.isopen);         poolsizetextfield = (edittext) getview().findviewbyid(r.id.poolsize);         commenttextfield = (edittext) getview().findviewbyid(r.id.comment);         metrictextfield = (edittext) getview().findviewbyid(r.id.metric);           date sessiondate = instabeattimeservice.getdatefromlong(session._date);         int sessionday = instabeattimeservice.getdayfromdate(sessiondate);         int sessionmonth = instabeattimeservice.getmonthfromdate(sessiondate);         int sessionyear = instabeattimeservice.getyearfromdate(sessiondate);         int sessionhour = instabeattimeservice.gethourfromdate(sessiondate);         int sessionminute = instabeattimeservice.getminutefromdate(sessiondate);          datefield  = (edittext) getview().findviewbyid(r.id.sessiondatefield);         dateformatter = new simpledateformat("mm/dd/yyyy", locale.us);          datefield.setinputtype(inputtype.type_null);         datefield.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view v) {                  datepickerdialog.show();             }         });         datefield.settext(sessionmonth + "/" + sessionday + "/" + sessionyear);          datepickerdialog = new datepickerdialog(getactivity(), new datepickerdialog.ondatesetlistener() {              public void ondateset(datepicker view, int year, int monthofyear, int dayofmonth) {                 calendar newdate = calendar.getinstance();                 newdate.set(year, monthofyear, dayofmonth);                 datefield.settext(dateformatter.format(newdate.gettime()));             }          },sessionyear, sessionmonth, sessionday);          timefield = (edittext) getview().findviewbyid(r.id.sessiontimefield);         //todo: set user preferences time format hh or kk         timeformatter = new simpledateformat("hh:mm", locale.us);          timefield.setinputtype(inputtype.type_null);         timefield.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view v) {                  timepickerdialog.show();             }         });         timefield.settext(sessionhour + ":" + sessionminute);          timepickerdialog = new timepickerdialog(getactivity(), new timepickerdialog.ontimesetlistener() {              public void ontimeset(timepicker view,  int hourofday, int minute) {                 calendar newtime = calendar.getinstance();                 int hr = newtime.get(calendar.hour_of_day);                 int mn = newtime.get(calendar.minute);                 /*todo: set user preferences time format hh or kk */                 datefield.settext(hr+":"+mn);             }          },sessionhour, sessionminute, true/*todo: set user preferences time format hh or kk */);         isopentextfield.settext(session._isopen+"");         metrictextfield.settext(session._metric);         commenttextfield.settext(session._comment);         poolsizetextfield.settext("" + session._poolsize);     } 

activity , fragment lifecycle not trivial on android. please remember activity , fragment destroyed , recreated on device rotation so,if need method not called again can use oncreate method of fragment , put setretaininstancestate(true) inside same method. in way fragment retained , not destroyed on device orientation changes. must define fragment in xml layout , must assign id, if layout added programmaticcally or not have ui can use fragmentmanager , tag add , retrieve fragment.

you can check on android handling runtime changes guide