android - Get the nearest location to user from Json -


i'm new android, i'm creating app nearest geocaches device's current location..

i have bit of code : 

public class mainactivity extends fragmentactivity { private googlemap map; textview test; private arraylist<latlng> markers = new arraylist<latlng>();  // main code. @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     strictmode.threadpolicy policy = new strictmode.threadpolicy.builder()             .permitall().build();     strictmode.setthreadpolicy(policy);      test = (textview) findviewbyid(r.id.test);      string result = json             .getresult("http://www.student.soc.napier.ac.uk/~40053830/cms/markers.php");      map = ((supportmapfragment) getsupportfragmentmanager()             .findfragmentbyid(r.id.map)).getmap();     map.setmylocationenabled(true);      try {         jsonarray jarray = new jsonarray(result);          (int j = 0; j < jarray.length(); j++) {             jsonobject json_data = jarray.getjsonobject(j);             latlng tmp = new latlng(double.parsedouble(json_data                     .getstring("latitude")), double.parsedouble(json_data                     .getstring("longitude")));             map.addmarker(new markeroptions().position(tmp).title(                     json_data.getstring("name")));             markers.add(tmp);         }     } catch (jsonexception e) {         log.e("log_tag", "error parsing data " + e.tostring());     }     location mylocation = map.getmylocation();     location nearest = new location("nearest");     nearest.setlatitude(markers.get(0).latitude);     nearest.setlongitude(markers.get(0).longitude);     float distance = mylocation.distanceto(nearest);     (int = 1; < markers.size(); i++) {         location target = new location("target");         target.setlatitude(markers.get(i).latitude);         target.setlongitude(markers.get(i).longitude);          if (mylocation.distanceto(target) < distance) {             nearest = target;             distance = mylocation.distanceto(target);         }     }     test.settext((string.format("%.02f", distance * 0.000621371192))); }

i can't seem distance nearest on textview..

here's logcat :

08-18 19:01:50.463: e/androidruntime(16421): fatal exception: main 08-18 19:01:50.463: e/androidruntime(16421): process:         com.finlaysmith.motorcycleparking, pid: 16421 08-18 19:01:50.463: e/androidruntime(16421): java.lang.runtimeexception: unable start activity componentinfo{com.finlaysmith.motorcycleparking/com.finlaysmith.motorcycleparking.mainactivity}: java.lang.nullpointerexception 08-18 19:01:50.463: e/androidruntime(16421):    @ android.app.activitythread.performlaunchactivity(activitythread.java:2184) 08-18 19:01:50.463: e/androidruntime(16421):    @ android.app.activitythread.handlelaunchactivity(activitythread.java:2233) 08-18 19:01:50.463: e/androidruntime(16421):    @ android.app.activitythread.access$800(activitythread.java:135) 08-18 19:01:50.463: e/androidruntime(16421):    @ android.app.activitythread$h.handlemessage(activitythread.java:1196) 08-18 19:01:50.463: e/androidruntime(16421):    @ android.os.handler.dispatchmessage(handler.java:102) 08-18 19:01:50.463: e/androidruntime(16421):    @ android.os.looper.loop(looper.java:136) 08-18 19:01:50.463: e/androidruntime(16421):    @ android.app.activitythread.main(activitythread.java:5001) 08-18 19:01:50.463: e/androidruntime(16421):    @ java.lang.reflect.method.invokenative(native method) 08-18 19:01:50.463: e/androidruntime(16421):    @ java.lang.reflect.method.invoke(method.java:515) 08-18 19:01:50.463: e/androidruntime(16421):    @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:785) 08-18 19:01:50.463: e/androidruntime(16421):    @ com.android.internal.os.zygoteinit.main(zygoteinit.java:601) 08-18 19:01:50.463: e/androidruntime(16421):    @ dalvik.system.nativestart.main(native method) 08-18 19:01:50.463: e/androidruntime(16421): caused by: java.lang.nullpointerexception 08-18 19:01:50.463: e/androidruntime(16421):    @ com.finlaysmith.motorcycleparking.mainactivity.oncreate(mainactivity.java:66) 08-18 19:01:50.463: e/androidruntime(16421):    @ android.app.activity.performcreate(activity.java:5231) 08-18 19:01:50.463: e/androidruntime(16421):    @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1087) 08-18 19:01:50.463: e/androidruntime(16421):    @ android.app.activitythread.performlaunchactivity(activitythread.java:2148)

i know it's " float distance.. can't find how resolve it..

thanks

map.mylocation returning null because hasn't found location yet. may take time. need check null , not part of code if return null (you can later, once has location).


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