Notify user about location updates automatically android -

i'm trying android hive's tutorial understand how track location of user , show them places nearby. want notify user location change , redirect them first screen of app. have tried calling class contains notification code onlocationchanged method, shows null pointer exception @ pendingintent.getactivity().i have added permissions in manifest file here's code:

gpstracker.java:

this file contain onlocationchanged i'm trying call shownotif(). public class gpstracker extends service implements locationlistener {

private final context mcontext; notif n = new notif(); // flag gps status boolean isgpsenabled = false;  // flag network status boolean isnetworkenabled = false;  // flag gps status boolean cangetlocation = false;  location location = null; // location double latitude; // latitude double longitude; // longitude  // minimum distance change updates in meters private static final long min_distance_change_for_updates = 0;  // minimum time between updates in milliseconds private static final long min_time_bw_updates = 0;  // declaring location manager protected locationmanager locationmanager;  public gpstracker(context context) {     this.mcontext = context;     getlocation(); }  public location getlocation() {     try {         locationmanager = (locationmanager) mcontext                 .getsystemservice(location_service);          // getting gps status         isgpsenabled = locationmanager                 .isproviderenabled(locationmanager.gps_provider);          // getting network status         isnetworkenabled = locationmanager                 .isproviderenabled(locationmanager.network_provider);          if (!isgpsenabled && !isnetworkenabled) {             // no network provider enabled         } else {             this.cangetlocation = true;             if (isnetworkenabled) {                 locationmanager.requestlocationupdates(                         locationmanager.network_provider,                         min_time_bw_updates,                         min_distance_change_for_updates, this);                 log.d("network", "network enabled");                 if (locationmanager != null) {                     location = locationmanager                             .getlastknownlocation(locationmanager.network_provider);                     if (location != null) {                         latitude = location.getlatitude();                         longitude = location.getlongitude();                     }                 }             }             // if gps enabled lat/long using gps services             if (isgpsenabled) {                 if (location == null) {                     locationmanager.requestlocationupdates(                             locationmanager.gps_provider,                             min_time_bw_updates,                             min_distance_change_for_updates, this);                     log.d("gps", "gps enabled");                     if (locationmanager != null) {                         location = locationmanager                                 .getlastknownlocation(locationmanager.gps_provider);                         if (location != null) {                             latitude = location.getlatitude();                             longitude = location.getlongitude();                         }                     }                 }             }         }         toast.maketext(getapplicationcontext(), "location changed",toast.length_short).show();      } catch (exception e) {         e.printstacktrace();     }      return location; }  /**  * stop using gps listener calling function stop using gps in  * app  * */ public void stopusinggps() {     if (locationmanager != null) {         locationmanager.removeupdates(gpstracker.this);     } }  /**  * function latitude  * */ public double getlatitude() {     if (location != null) {         latitude = location.getlatitude();     }      // return latitude     return latitude; }  /**  * function longitude  * */ public double getlongitude() {     if (location != null) {         longitude = location.getlongitude();     }      // return longitude     return longitude; }  /**  * function check gps/wifi enabled  *  * @return boolean  * */ public boolean cangetlocation() {     return this.cangetlocation; }  /**  * function show settings alert dialog on pressing settings button  * lauch settings options  * */ public void showsettingsalert() {     alertdialog.builder alertdialog = new alertdialog.builder(mcontext);      // setting dialog title     alertdialog.settitle("gps settings");      // setting dialog message     alertdialog             .setmessage("gps not enabled. want go settings menu?");      // on pressing settings button     alertdialog.setpositivebutton("settings",             new dialoginterface.onclicklistener() {                 public void onclick(dialoginterface dialog, int which) {                     intent intent = new intent(                             settings.action_location_source_settings);                     mcontext.startactivity(intent);                 }             });      // on pressing cancel button     alertdialog.setnegativebutton("cancel",             new dialoginterface.onclicklistener() {                 public void onclick(dialoginterface dialog, int which) {                     dialog.cancel();                 }             });      // showing alert message     alertdialog.show(); }  @override public void onlocationchanged(location location) {         //notification     if(location!=null) {         n.shownotif(this);     }  }  @override public void onproviderdisabled(string provider) { }  @override public void onproviderenabled(string provider) { }  @override public void onstatuschanged(string provider, int status, bundle extras) { }  @override public ibinder onbind(intent arg0) {     return null; } 

}

this notif.java

public class notif { void shownotif(context context) {      pendingintent pi = pendingintent.getactivity(context, 0, new intent(context, mainactivity.class), 0);     notification noti = new notificationcompat.builder(context)             .setcontenttitle("notification")             .setcontenttext("there new places visit")             .setsmallicon(android.r.drawable.stat_sys_warning)             .setcontentintent(pi)             .setdefaults(notification.default_sound)             .setdefaults(notification.default_vibrate)             .setwhen(system.currenttimemillis())             .setautocancel(true)             .build();     notificationmanager mgr = (notificationmanager)context.getsystemservice(context.notification_service);     mgr.notify(0,noti); } 

}

and mainactivity.java oncreate method

    @override public void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);      cd = new connectiondetector(getapplicationcontext());      // check if internet present     isinternetpresent = cd.isconnectingtointernet();     if (!isinternetpresent) {         // internet connection not present         alert.showalertdialog(mainactivity.this, "internet connection error",                 "please connect working internet connection", false);         // stop executing code return         return;     }      // creating gps class object     gps = new gpstracker(this);      // check if gps location can     if (gps.cangetlocation()) {         log.d("your location", "latitude:" + gps.getlatitude() + ", longitude: " + gps.getlongitude());     } else {         // can't user's current location         alert.showalertdialog(mainactivity.this, "gps status",                 "couldn't location information. please enable gps",                 false);         // stop executing code return         return;     }      // getting listview     lv = (listview) findviewbyid(r.id.list);      // button show on map     btnshowonmap = (button) findviewbyid(r.id.btn_show_map);      // calling background async task load google places     // after getting places google data shown in listview     new loadplaces().execute();      /** button click event shown on map */     btnshowonmap.setonclicklistener(new view.onclicklistener() {          @override         public void onclick(view arg0) {             intent = new intent(getapplicationcontext(),                     placesmapactivity.class);             // sending user current geo location             i.putextra("user_latitude", double.tostring(gps.getlatitude()));             i.putextra("user_longitude", double.tostring(gps.getlongitude()));              // passing near places map activity             i.putextra("near_places", nearplaces);             // staring activity             startactivity(i);         }     });       /**      * listitem click event      * on selecting listitem singleplaceactivity launched      * */     lv.setonitemclicklistener(new onitemclicklistener() {          @override         public void onitemclick(adapterview<?> parent, view view,                                 int position, long id) {             // getting values selected listitem             string reference = ((textview) view.findviewbyid(r.id.reference)).gettext().tostring();              // starting new intent             intent in = new intent(getapplicationcontext(),                     singleplaceactivity.class);              // sending place refrence id single place activity             // place refrence id used "place full details"             in.putextra(key_reference, reference);             startactivity(in);         }     }); } 

i have tried calling class contains notification code onlocationchanged method, shows null pointer exception @ pendingintent.getactivity().

pendingintent pi = pendingintent.getactivity(context, 0, new intent(context, mainactivity.class), 0); 

as getting getting null in context , pass mcontext inside onlocationchanged .e.g

    @override public void onlocationchanged(location location) {         //notification     if(location!=null) {         n.shownotif(mcontext);     }