Android Async Task Error -

i new in android , practicing sms app asynctask. when run on emulator app not start. error occurs fatal exception asynctask #1. i'm trying fill inbox using asynctask. plz help.

public class welcome extends activity implements onclicklistener{ listview smslist; cursor cursor; context context; simplecursoradapter mcursor; button button; private static final string tag = "ada class"; private static final string tag1 = "adapte class";  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_welcome);     button= (button) findviewbyid(r.id.button1);     button.setonclicklistener(this);     smslist = (listview) findviewbyid(r.id.listview1);      new thrd().execute(context); }      class thrd extends asynctask<context,void,simplecursoradapter>{         string [] a= {"address", "body","date"};         int[] b={r.id.textview1,r.id.textview2,r.id.textview4};         @override         protected simplecursoradapter doinbackground(context... params) {             context c= params[0];             uri smsuri = uri.parse("content://sms/inbox");             cursor=getcontentresolver().query(smsuri, null, null ,null,null);             mcursor=new simplecursoradapter(c, r.layout.row, cursor, a,b, 0);             return mcursor;         }          @override         protected void onpostexecute(simplecursoradapter result) {             smslist.setadapter(result);         }     }  @override public void onclick(view v) {     intent intent=new intent(this, sendsms.class);     startactivity(intent);  } 

}

please check value of context.

context = getapplicationcontext();