android - Notification.setStyle crashes and not able to set lock screen -

i trying make custom notification , following ian lake tutorial in media player , following tutorial in google set notification .set style getting crashed if dont use not able make media player lock screen trying.

private void initmediasession() throws remoteexception {     if (mediasessionmanager != null) return; //mediasessionmanager exists     componentname mediabuttonreceiver = new componentname(getapplicationcontext(), mediabuttonreceiver.class);      mediasession = new mediasessioncompat(getapplicationcontext(), "audioplayer", mediabuttonreceiver, null);     //get mediasessions transport controls     transportcontrols = mediasession.getcontroller().gettransportcontrols();     //set mediasession -> ready receive media commands     mediasession.setactive(true);     //indicate mediasession handles transport control commands     // through mediasessioncompat.callback.     mediasession.setflags(mediasessioncompat.flag_handles_media_buttons | mediasessioncompat.flag_handles_transport_controls);     intent mediabuttonintent = new intent(intent.action_media_button);     mediabuttonintent.setclass(this, mediabuttonreceiver.class);     pendingintent pendingintent = pendingintent.getbroadcast(this, 0, mediabuttonintent, 0);     mediasession.setmediabuttonreceiver(pendingintent);     //set mediasession's metadata     updatemetadata();     // passing data       // attach callback receive mediasession updates     mediasession.setcallback(new mediasessioncompat.callback() {         // implement callbacks         @override         public void onplay() {             super.onplay();             messagesent();             = false;             resumemedia();             buildnotification(playbackstatus.playing);         }          @override         public void onpause() {             super.onpause();             messagesent();             = true;             pausemedia();             buildnotification(playbackstatus.paused);         }          @override         public void onskiptonext() {             super.onskiptonext();              skiptonext();             updatemetadata();             buildnotification(playbackstatus.playing);         }          @override         public void onskiptoprevious() {             super.onskiptoprevious();              skiptoprevious();             updatemetadata();             buildnotification(playbackstatus.playing);         }          @override         public void onstop() {             super.onstop();             removenotification();             //stop service             pausemedia();             messagesent();             stopself();         }          @override         public void onseekto(long position) {             super.onseekto(position);         }     }); }  private void updatemetadata() {     //replace medias albumart     // update current metadata     mediametadatacompat.builder metadatabuilder = new mediametadatacompat.builder();      string artist;     if (activeaudio.getartist() != null) {         artist = activeaudio.getartist();     } else {         artist = "unknown";     }     string album;     if (activeaudio.getalbum() != null) {         album = activeaudio.getalbum();     } else {         album = "album";     }     bitmap albumart;     uri myuri = uri.parse(activeaudio.getalbum_art());     try {         inputstream image_stream = getcontentresolver().openinputstream(myuri);         bitmap bitmap = bitmapfactory.decodestream(image_stream);         if (bitmap != null) {             albumart = bitmap;         } else {             albumart = bitmapfactory.decoderesource(getresources(),                     r.drawable.music);         }      } catch (filenotfoundexception e) {         e.printstacktrace();         albumart = bitmapfactory.decoderesource(getresources(),                 r.drawable.music);     }     metadatabuilder.putbitmap(mediametadatacompat.metadata_key_display_icon, albumart);     metadatabuilder.putbitmap(mediametadatacompat.metadata_key_album_art, albumart);      //lock screen icon pre lollipop     metadatabuilder.putbitmap(mediametadatacompat.metadata_key_art, albumart);     metadatabuilder.putstring(mediametadatacompat.metadata_key_display_title, activeaudio.gettitle());     metadatabuilder.putstring(mediametadatacompat.metadata_key_display_subtitle, activeaudio.getalbum());     metadatabuilder.putstring(mediametadatacompat.metadata_key_album, album);     metadatabuilder.putlong(mediametadatacompat.metadata_key_track_number, 1);     metadatabuilder.putlong(mediametadatacompat.metadata_key_num_tracks, 1);      mediasession.setmetadata(metadatabuilder.build()); }  private void buildnotification(playbackstatus playbackstatus) {      /**      * notification actions -> playbackaction()      *  0 -> play      *  1 -> pause      *  2 -> next track      *  3 -> previous track      */      mediacontrollercompat controller = mediasession.getcontroller();     mediametadatacompat mediametadata = controller.getmetadata();     mediadescriptioncompat description = mediametadata.getdescription();      remoteviews views = new remoteviews(getpackagename(),             r.layout.customnotification);       if (playbackstatus == playbackstatus.playing || singleton.getinstance().getmedia() == 1) {         views.setimageviewresource(r.id.imagebutton2,                 r.drawable.ic_pause_circle_outline_white_48dp);          messagesent();          views.setonclickpendingintent(r.id.imagebutton2, playbackaction(1));      } else if (playbackstatus == playbackstatus.paused || singleton.getinstance().getmedia() == 2) {         views.setimageviewresource(r.id.imagebutton2,                 r.drawable.ic_play_circle_outline_white_48dp);         messagesent();          views.setonclickpendingintent(r.id.imagebutton2, playbackaction(0));      }      views.setviewvisibility(r.id.imageview, view.visible);      // intent notificationintent = new intent(this, main2activity.class);      // pendingintent pendingintent = pendingintent.getactivity(this, 0,     //         notificationintent, pendingintent.flag_update_current);       views.setonclickpendingintent(r.id.imagebutton3, playbackaction(3));     views.setonclickpendingintent(r.id.imagebutton4, playbackaction(2));      views.setimageviewresource(r.id.imagebutton3,             r.drawable.ic_skip_previous_circle_outline_white_36dp);     views.setimageviewresource(r.id.imagebutton4,             r.drawable.ic_skip_next_circle_outline_white_36dp);     views.settextviewtext(r.id.textview, description.gettitle());     views.settextviewtext(r.id.textview2, description.getsubtitle());     views.setimageviewbitmap(r.id.imageview, description.geticonbitmap());       notificationcompat.builder sta = new notificationcompat.builder(this);    //  sta.setcontentintent(pendingintent);     sta.setcontent(views);     sta.setsmallicon(r.drawable.ic_audiotrack_white_24dp);     sta.setstyle(new notificationcompat.mediastyle().setshowactionsincompactview(0).setmediasession(mediasession.getsessiontoken()));       startforeground(constants.notification_id.foreground_service, sta.build());    }   public pendingintent playbackaction(int actionnumber) {     intent playbackaction = new intent(this, mediaservice.class);     switch (actionnumber) {         case 0:             // play             playbackaction.setaction(action_play);             return pendingintent.getservice(this, actionnumber, playbackaction, 0);         case 1:             // pause             playbackaction.setaction(action_pause);             return pendingintent.getservice(this, actionnumber, playbackaction, 0);         case 2:             // next track             playbackaction.setaction(action_next);             return pendingintent.getservice(this, actionnumber, playbackaction, 0);         case 3:             // previous track             playbackaction.setaction(action_previous);             return pendingintent.getservice(this, actionnumber, playbackaction, 0);         case 4:             playbackaction.setaction(constants.action.stopforeground_action);             return pendingintent.getservice(this, actionnumber, playbackaction, 0);         default:             break;     }     return null; }  private void removenotification() {     try {         stopforeground(true);     } catch (exception e) {         e.printstacktrace();     }   }  private void handleincomingactions(intent playbackaction) {     if (playbackaction == null || playbackaction.getaction() == null) return;      string actionstring = playbackaction.getaction();     if (actionstring.equalsignorecase(action_play)) {         transportcontrols.play();     } else if (actionstring.equalsignorecase(action_pause)) {         transportcontrols.pause();     } else if (actionstring.equalsignorecase(action_next)) {         transportcontrols.skiptonext();     } else if (actionstring.equalsignorecase(action_previous)) {         transportcontrols.skiptoprevious();     } else if (actionstring.equalsignorecase(action_stop)) {         transportcontrols.stop();     } else if (actionstring.equalsignorecase(constants.action.stopforeground_action)) {         transportcontrols.stop();     } } 

the notification working fine add style not showing lock screen , when add style getting crashed .i dont understand how show lockscreen , why getting crashed when using style.