java - Calling MainActivity method from other classes (which extend broadcast receiver) -

i'm trying call method display_notification of mainactivity other class (phonestatereceiver).

but got error:

java.lang.runtimeexception: unable start receiver com.weekendproject.roshu.spamblocker.phonestatereceiver: java.lang.nullpointerexception: attempt invoke virtual method 'java.lang.string android.content.context.getpackagename()' on null object reference

error specially pointed line in mainactivity

intent resultintent = new intent(getapplicationcontext(), mainactivity.class);

however tried change getapplicationcontext() "this" , "getactivity()", not working

here complete code

mainactivity.java

public class mainactivity extends actionbaractivity {      public void display_notification(string incoming_number) {      notificationcompat.builder mbuilder =             new notificationcompat.builder(getapplicationcontext())                     .setsmallicon(r.drawable.ic_action)                     .setcontenttitle("spamblocker alert !!")                     .setcontenttext("spamblocker blocked number : " + incoming_number);      // **error occured in following line**     intent resultintent = new intent(getapplicationcontext(), mainactivity.class);      taskstackbuilder stackbuilder = taskstackbuilder.create(getapplicationcontext());     stackbuilder.addparentstack(mainactivity.class);     stackbuilder.addnextintent(resultintent);     pendingintent resultpendingintent =             stackbuilder.getpendingintent(                     0,                     pendingintent.flag_update_current             );     mbuilder.setcontentintent(resultpendingintent);     notificationmanager mnotificationmanager =             (notificationmanager) getsystemservice(context.notification_service);     random r = new random();     int rand = r.nextint(1000);     mnotificationmanager.notify(rand, mbuilder.build());     } } 

phonestatereceiver.java

public class phonestatereceiver extends broadcastreceiver {      mainactivity mactivity;      @override     public void onreceive(context context, intent intent) {         mactivity = new mainactivity();         mactivity.display_notification(incomingnumber);           // call main activity methods      } } 

you not using context provided onreceive. try passing context display_notification rather using activity's context might not running @ time receive broadcast.

so change method signature this:

 public void display_notification(string incoming_number, context context)  

and, pass context onreceive this:

 mactivity.display_notification(incomingnumber, context); 

and use context when pass intent this:

 intent resultintent = new intent(context, mainactivity.class); 

edited

either put entire method in receiver , use context provided onreceive

or,

change line this:

notificationmanager mnotificationmanager =         (notificationmanager) context.getsystemservice(context.notification_service); 

important part is, context.getsystemservice, context onreceive.