java - Calculating distance between two points -

i know has been asked loads before, i'm getting mixed views on whats correct , whats not,

i trying calculate distance between 2 points in app using 2 buttons, start , stop.

i figured simple, lat , long of position when start pressed, them again when stop pressed, calculate 2 , voila. isn't going plan.

i have set dialog on stop button when clicked feedback , i'm returning (presumably) single latitude or longitude.

my codes below::

 public class maprun extends fragmentactivity implements locationlistener,             locationsource {         private onlocationchangedlistener mlistener;         private locationmanager locationmanager;          private googlemap mmap;         double lat, lng;         static double startlat;         double startlong;         double stoplat;         double stoplong;         public static location l;          @override         protected void oncreate(bundle savedinstancestate) {             super.oncreate(savedinstancestate);             setcontentview(r.layout.maprun);              locationmanager = (locationmanager) getsystemservice(location_service);             // creating criteria object retrieve provider             criteria criteria = new criteria();              // getting name of best provider             string provider = locationmanager.getbestprovider(criteria, true);              // getting current location             location location = locationmanager.getlastknownlocation(provider);              l = location;             lat = l.getlatitude();             lng = l.getlongitude();              onlocationchanged(location);             locationmanager.requestlocationupdates(provider, 20000, 0, this);              setupmapifneeded();         }          @override         public void onpause() {             if (locationmanager != null) {                 locationmanager.removeupdates(this);             }              super.onpause();         }          @override         public void onresume() {             super.onresume();              setupmapifneeded();              if (locationmanager != null) {                 mmap.setmylocationenabled(true);             }         }          /**          * sets map if possible (i.e., google play          * services apk correctly installed) , map has not been          * instantiated.. ensure ever call          * {@link #setupmap()} once when {@link #mmap} not null.          * <p>          * if isn't installed {@link supportmapfragment} (and          * {@link com.google.android.gms.maps.mapview mapview}) show prompt          * user install/update google play services apk on          * device.          * <p>          * user can return activity after following prompt ,          * correctly installing/updating/enabling google play services. since          * activity may not have been destroyed during process          * (it stopped or paused),          * {@link #oncreate(bundle)} may not called again should call          * method in {@link #onresume()} guarantee called.          */         private void setupmapifneeded() {             // null check confirm have not instantiated             // map.             if (mmap == null) {                 // try obtain map supportmapfragment.                 mmap = ((supportmapfragment) getsupportfragmentmanager()                         .findfragmentbyid(r.id.map)).getmap();                 // check if successful in obtaining map.                  if (mmap != null) {                     setupmap();                 }                  // how register locationsource                 mmap.setlocationsource(this);             }         }          /**          * can add markers or lines, add listeners or move          * camera. in case, add marker near africa.          * <p>          * should called once , when sure {@link #mmap}          * not null.          */         private void setupmap() {             mmap.setmylocationenabled(true);         }          @override         public void activate(onlocationchangedlistener listener) {             mlistener = listener;         }          @override         public void deactivate() {             mlistener = null;         }          @override         public void onlocationchanged(location location) {             if (mlistener != null) {                 mlistener.onlocationchanged(location);                  // move camera user's location once it's available!                  mmap.animatecamera(cameraupdatefactory.newlatlngzoom(new latlng(                         location.getlatitude(), location.getlongitude()), 16.0f));             }         }          @override         public void onproviderdisabled(string provider) {             // todo auto-generated method stub             toast.maketext(this, "provider disabled", toast.length_short).show();         }          @override         public void onproviderenabled(string provider) {             // todo auto-generated method stub             toast.maketext(this, "provider enabled", toast.length_short).show();         }          @override         public void onstatuschanged(string provider, int status, bundle extras) {             // todo auto-generated method stub             toast.maketext(this, "status changed", toast.length_short).show();         }             @override         public boolean oncreateoptionsmenu(menu menu) {             super.oncreateoptionsmenu(menu);             menuinflater inflater = getmenuinflater();             inflater.inflate(r.menu.map_menu, menu);             return true;         }          @override         public boolean onoptionsitemselected(menuitem item) {             switch (item.getitemid()) {             case r.id.startrun:                  startrun();             case r.id.stoprun:                  stoprun();                  return true;              default:                 return super.onoptionsitemselected(item);             }          }          public void startrun() {             ;            }          public void stoprun() {             location startpoint = new location("ran from");              startpoint.setlatitude(lat);             startpoint.setlongitude(lng);              location stoppoint = new location("ran to");             stoppoint.setlatitude(stoplat);             stoppoint.setlongitude(stoplong);             float distance = startpoint.distanceto(stoppoint);             string diststr = string.valueof(distance);             dialog d = new dialog(this);             d.settitle("distance");             textview tv = new textview(this);             tv.settext(diststr);             d.setcontentview(tv);             d.show();          } 

here updated buttons far, i've got principle think i'm struggling correct way store , pass variables:

@override     public boolean onoptionsitemselected(menuitem item) {         switch (item.getitemid()) {         case r.id.startrun:             currentlocation = lat + lng;             startlocation = currentlocation;          case r.id.stoprun:             currentlocation = lat + lng;             stoplocatio 

n = currentlocation;

        float distance = startlocation.distanceto(stoplocation);         string diststr = string.valueof(distance);         dialog d = new dialog(this);         d.settitle("distance");         textview tv = new textview(this);         tv.settext(diststr);         d.setcontentview(tv);         d.show();          return true;      default:         return super.onoptionsitemselected(item);     } 

and onlocationchanged:

@override     public void onlocationchanged(location location) {         l = location;         lat = l.getlatitude();         lng = l.getlongitude();         if (mlistener != null) {             mlistener.onlocationchanged(location);              // move camera user's location once it's available!              mmap.animatecamera(cameraupdatefactory.newlatlngzoom(new latlng(                     location.getlatitude(), location.getlongitude()), 16.0f));         }     } 

location has distanceto. register location gps, when user press start. when user press stop, current location , do:

currentlocation.distanceto(firstlocation) ; 

distanceto returns float represent approximate distance in meters between location , given location

public class maprun extends fragmentactivity implements locationlistener,         locationsource {     location startlocation;    location endlocation;     location currentlocation;       @override     public void onlocationchanged(location location) {         if (mlistener != null) {             mlistener.onlocationchanged(location);              // move camera user's location once it's available!              mmap.animatecamera(cameraupdatefactory.newlatlngzoom(new latlng(                     location.getlatitude(), location.getlongitude()), 16.0f));         }        currentlocation = location;     }   public void startrun() {         startlocation = currentlocation;     }      public void stoprun() {        stoplocation = currentlocation;     }   public float getdistance() {    float distance = 0f;    if (stoplocation != null && startlocation != null)        distance = stoplocation.distanceto(startlocation);    return distance;  }  }