java - Why am I getting this error? Please see the details -

i'm developing material design app & applying activity transition have written following code in mainactivity.java

my mainactivity.java file's code:

public class mainactivity extends appcompatactivity {      public toolbar toolbar;     public tablayout tablayout;     public viewpager viewpager;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         if (build.version.sdk_int >= build.version_codes.lollipop) {             // call material design apis here             // enable transitions             getwindow().requestfeature(window.feature_content_transitions);         } else {          }         setcontentview(r.layout.activity_main);          spannablestring s = new spannablestring("abc");         s.setspan(new typefacespan(this, "pacifico.ttf"), 0, s.length(),                 spannable.span_exclusive_exclusive);          toolbar = (toolbar) findviewbyid(r.id.toolbar);         setsupportactionbar(toolbar);          getsupportactionbar().setdisplayhomeasupenabled(false);         getsupportactionbar().settitle(s);          viewpager = (viewpager) findviewbyid(r.id.viewpager);         setupviewpager(viewpager);          tablayout = (tablayout) findviewbyid(r.id.tabs);         tablayout.setupwithviewpager(viewpager);         customtabfont();      }      private void customtabfont() {          string fontpath = "fonts/pacifico.ttf";          typeface tf = typeface.createfromasset(getassets(), fontpath);          textview tabone = (textview) layoutinflater.from(this).inflate(r.layout.custom_tab, null);         tabone.settext("accept request");         tabone.settypeface(tf);         tablayout.gettabat(0).setcustomview(tabone);          textview tabtwo = (textview) layoutinflater.from(this).inflate(r.layout.custom_tab, null);         tabtwo.settext("post request");         tabtwo.settypeface(tf);         tablayout.gettabat(1).setcustomview(tabtwo);      }      private void setupviewpager(viewpager viewpager) {         viewpageradapter adapter = new viewpageradapter(getsupportfragmentmanager());         adapter.addfragment(new acceptarequest(), "accept request");         adapter.addfragment(new postarequest(), "post request");         viewpager.setadapter(adapter);     }      class viewpageradapter extends fragmentpageradapter {         private final list<fragment> mfragmentlist = new arraylist<>();         private final list<string> mfragmenttitlelist = new arraylist<>();          public viewpageradapter(fragmentmanager manager) {             super(manager);         }          @override         public fragment getitem(int position) {             return mfragmentlist.get(position);         }          @override         public int getcount() {             return mfragmentlist.size();         }          public void addfragment(fragment fragment, string title) {             mfragmentlist.add(fragment);             mfragmenttitlelist.add(title);         }          @override         public charsequence getpagetitle(int position) {             return mfragmenttitlelist.get(position);         }     }      @override     public boolean oncreateoptionsmenu(menu menu) {         // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.menu_main, menu);         return true;     }      @override     public boolean onoptionsitemselected(menuitem item) {         // handle action bar item clicks here. action bar         // automatically handle clicks on home/up button, long         // specify parent activity in androidmanifest.xml.         int id = item.getitemid();          //noinspection simplifiableifstatement         if (id == r.id.action_profile) {             // check if we're running on android 5.0 or higher             if (build.version.sdk_int >= build.version_codes.lollipop) {                 // call material design apis here                 getwindow().setexittransition(new explode());                 intent profileintent = new intent(mainactivity.this, profileactivity.class);                 startactivity(profileintent, activityoptions                         .makescenetransitionanimation(this).tobundle());             } else {                 // implement feature without material design                 intent profileintent = new intent(mainactivity.this, profileactivity.class);                 startactivity(profileintent);             }         } else if (id == r.id.action_settings) {             intent settingsintent = new intent(mainactivity.this, settingsactivity.class);             startactivity(settingsintent);         } else if (id == r.id.action_help) {             intent helpintent = new intent(intent.action_send);             intent chooser = intent.createchooser(helpintent, "choose app");             helpintent.putextra(intent.extra_email, new string[]{"help@abcxyz123.com"});             helpintent.settype("message/rfc822");             startactivity(chooser);         } else if (id == r.id.action_faqs) {             intent faqsintent = new intent(intent.action_view, uri.parse("http://www.abcxyz123.com/faqs"));             startactivity(faqsintent);         } else if (id == r.id.action_about) {             intent aboutintent = new intent(mainactivity.this, aboutactivity.class);             startactivity(aboutintent);         }          return super.onoptionsitemselected(item);     } } 

after running app, i'm getting following error:

android.util.androidruntimeexception: requestfeature() must called before adding content must called before adding content. 

i not understand why getting error when have added requestfeature() before adding content?

please let me know.

i'm new stackoverflow, please cooperate.

thanks in advance.

your activity extends appcompatactivity extensive setup in oncreate(). call requestfeature() before calling super.oncreate().