android - When I click start button for proximity responce It crashes my app -

when click on button, calls setproximityalert() function, , toast displayed. not understand problem is,

@override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.locations);      button start = (button) findviewbyid(r.id.startl);     start.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             setproximityalert();             toast.maketext(getbasecontext(), "started", toast.length_long).show();          }     });  }  private static final string mmh_proximity_alert = "com.example.proximityalert"; private void setproximityalert() {     cursor c = db.rawquery("select * locations", null);      double lng = c.getdouble(c.getcolumnindex("longitude"));     c.movetonext();      double lat = c.getdouble(c.getcolumnindex("latitude"));     c.movetonext();      float rds = c.getfloat(c.getcolumnindex("radius"));     c.movetonext();      string locservice = context.location_service;     locationmanager locationmanager;     locationmanager = (locationmanager)getsystemservice(locservice);      long expiration = -1; // not expire     intent intent = new intent(mmh_proximity_alert);     pendingintent proximityintent = pendingintent.getbroadcast(this, -1, intent, 0);     locationmanager.addproximityalert(lat, lng, rds, expiration, proximityintent);     c.close();      locationmanager.addproximityalert(         lat, // latitude of central point of alert region         lng, // longitude of central point of alert region         rds, // radius of central point of alert region, in meters         expiration, // time proximity alert, in milliseconds, or -1 indicate no                           expiration         proximityintent // used generate intent fire when entry or exit alert region detected     );      intentfilter filter = new intentfilter(mmh_proximity_alert);     registerreceiver(new proximityintentreceiver(), filter); } 

use movetofirst method on cursor before try access data.