Android, trying to find logic to store latitude and longitude values from user location

Question

As stated in the question, I would like to save lat and longitude as a double so I can use them in my program.

I can use setOnMyLocationChange listener, and from there create an object from the UserLocation class I have created which stores the lat and long.

I can print it out within the listener method using UserLocation.getLat() but I can not store the variable to use it elsewhere in the program. I will post the code which I think is relevant.

I have UserLocation l stored as global variable

UserLocation l;

Here I am getting a null object reference for l.getLat() even though I can reference the variable in the listener.

else if (city.equals("myLocation")) {

            map.setMyLocationEnabled(true);
            Location myLocation = map.getMyLocation();
            map.setOnMyLocationChangeListener(this);
//            map.setOnMyLocationChangeListener(null);
            lat = l.getLat();
            lon = l.getLng();
            Toast.makeText(this, lat+" is latMy in map activity ", Toast.LENGTH_LONG).show();


        }

Here I can print out the values just fine

  @Override
    public void onMyLocationChange(Location location) {

        latMy = location.getLatitude();
         lngMy = location.getLongitude();
        l = new UserLocation();
        l.setLat(latMy);
        l.setLng(lngMy);
        Toast.makeText(this, latMy+" is latMy in LOCATION CHANGE ", Toast.LENGTH_LONG).show();

    }

Here is my UserLocation class

package com.example.its.citymap;

public class UserLocation {
    private double lat; 
    private double lng; 

    public double getLat() {
        return lat;
    }

    public void setLat(double lat) {
        this.lat = lat;
    }

    public double getLng() {
        return lng;
    }

    public void setLng(double lng) {
        this.lng = lng;
    }
}

I have searched and tried a lot but can not find a solid answer to this.

Thank you

Store that UserLocation in a class level variable. There isn't any trick to it. — Gabe Sechan, Nov 17 '16 at 05:27

score 0 · Answer 1 · edited Dec 05 '16 at 10:39

First of all I check what providers are enabled. Some may be disabled on the device, some may be disabled in application manifest.

If any provider is available I start location listeners and timeout timer. It's 20 seconds in my example, may not be enough for GPS so you can enlarge it.

If I get update from location listener I use the provided value. I stop listeners and timer.

If I don't get any updates and timer elapses I have to use last known values.

I grab last known values from available providers and choose the most recent of them.

Here's how I use my class:

LocationResult locationResult = new LocationResult(){
    @Override
    public void gotLocation(Location location){
        //Got the location!
    }
};
MyLocation myLocation = new MyLocation();
myLocation.getLocation(this, locationResult);
And here's MyLocation class:

import java.util.Timer;
import java.util.TimerTask;
import android.content.Context;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;

public class MyLocation {
    Timer timer1;
    LocationManager lm;
    LocationResult locationResult;
    boolean gps_enabled=false;
    boolean network_enabled=false;

    public boolean getLocation(Context context, LocationResult result)
    {
        //I use LocationResult callback class to pass location value from MyLocation to user code.
        locationResult=result;
        if(lm==null)
            lm = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);

        //exceptions will be thrown if provider is not permitted.
        try{gps_enabled=lm.isProviderEnabled(LocationManager.GPS_PROVIDER);}catch(Exception ex){}
        try{network_enabled=lm.isProviderEnabled(LocationManager.NETWORK_PROVIDER);}catch(Exception ex){}

        //don't start listeners if no provider is enabled
        if(!gps_enabled && !network_enabled)
            return false;

        if(gps_enabled)
            lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListenerGps);
        if(network_enabled)
            lm.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListenerNetwork);
        timer1=new Timer();
        timer1.schedule(new GetLastLocation(), 20000);
        return true;
    }

    LocationListener locationListenerGps = new LocationListener() {
        public void onLocationChanged(Location location) {
            timer1.cancel();
            locationResult.gotLocation(location);
            lm.removeUpdates(this);
            lm.removeUpdates(locationListenerNetwork);
        }
        public void onProviderDisabled(String provider) {}
        public void onProviderEnabled(String provider) {}
        public void onStatusChanged(String provider, int status, Bundle extras) {}
    };

    LocationListener locationListenerNetwork = new LocationListener() {
        public void onLocationChanged(Location location) {
            timer1.cancel();
            locationResult.gotLocation(location);
            lm.removeUpdates(this);
            lm.removeUpdates(locationListenerGps);
        }
        public void onProviderDisabled(String provider) {}
        public void onProviderEnabled(String provider) {}
        public void onStatusChanged(String provider, int status, Bundle extras) {}
    };

    class GetLastLocation extends TimerTask {
        @Override
        public void run() {
             lm.removeUpdates(locationListenerGps);
             lm.removeUpdates(locationListenerNetwork);

             Location net_loc=null, gps_loc=null;
             if(gps_enabled)
                 gps_loc=lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
             if(network_enabled)
                 net_loc=lm.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);

             //if there are both values use the latest one
             if(gps_loc!=null && net_loc!=null){
                 if(gps_loc.getTime()>net_loc.getTime())
                     locationResult.gotLocation(gps_loc);
                 else
                     locationResult.gotLocation(net_loc);
                 return;
             }

             if(gps_loc!=null){
                 locationResult.gotLocation(gps_loc);
                 return;
             }
             if(net_loc!=null){
                 locationResult.gotLocation(net_loc);
                 return;
             }
             locationResult.gotLocation(null);
        }
    }

    public static abstract class LocationResult{
        public abstract void gotLocation(Location location);
    }
}

Android, trying to find logic to store latitude and longitude values from user location

1 Answers1