java - Android GPS incorrect location data on query

Question

I am not using mock locations for this... In fact the code was working fine just last week.

I have an app that gathers GPS data and spits out a google maps link using X,Y coordinates generated by the application itself. I am not 100% sure why its not working the way it should be but when I request the app to make a google maps link based on the GPS location provided by the phone it tells me I am 5 - 6 blocks away from my point of origin (Where I actually am at the time) Not quite what I want it to do

Knowns:

• I have the proper permissions set up
• All of the code worked last week just fine

Here is the code to gather the GPS info:

        Toast.makeText(context, "Gathering GPS Data...", Toast.LENGTH_SHORT).show();
    gps = new gpsTracker(Settings.this);
    if(gps.canGetLocation()){
        try{
            gps.getLocation();
            lon = gps.getLongitude();
            lat = gps.getLatitude();
            Toast.makeText(getApplicationContext(), "Your location is - 
lat: " + lat + "
lon: " + lon, Toast.LENGTH_LONG).show();
        }
        catch(Exception  e){}
    }
    else{
        gps.showSettingsAlert();
    }

The class all of the above is pulling from:

import android.app.AlertDialog;
import android.app.Service;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.IBinder;
import android.provider.Settings;
import android.util.Log;

public class gpsTracker extends Service implements LocationListener {

private final Context mContext;

// flag for GPS status
boolean isGPSEnabled = false;

// flag for network status
boolean isNetworkEnabled = false;

// flag for GPS status
boolean canGetLocation = false;

Location location; // location
double latitude; // latitude
double longitude; // longitude

// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters

// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute

// Declaring a Location Manager
protected LocationManager locationManager;

public gpsTracker(Context context) {
    this.mContext = context;
    getLocation();
}

public Location getLocation() {
    try {
        locationManager = (LocationManager) mContext
                .getSystemService(LOCATION_SERVICE);

        // getting GPS status
        isGPSEnabled = locationManager
                .isProviderEnabled(LocationManager.GPS_PROVIDER);

        // getting network status
        isNetworkEnabled = locationManager
                .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

        if (!isGPSEnabled && !isNetworkEnabled) {
            // no network provider is enabled
        } else {
            this.canGetLocation = true;
            // First get location from Network Provider
            if (isNetworkEnabled) {
                locationManager.requestLocationUpdates(
                        LocationManager.NETWORK_PROVIDER,
                        MIN_TIME_BW_UPDATES,
                        MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                Log.d("Network", "Network");
                if (locationManager != null) {
                    location = locationManager
                            .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                    if (location != null) {
                        latitude = location.getLatitude();
                        longitude = location.getLongitude();
                    }
                }
            }
            // if GPS Enabled get lat/long using GPS Services
            if (isGPSEnabled) {
                if (location == null) {
                    locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    Log.d("GPS Enabled", "GPS Enabled");
                    if (locationManager != null) {
                        location = locationManager
                                .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
            }
        }

    } catch (Exception e) {
        e.printStackTrace();
    }

    return location;
}

/**
 * Stop using GPS listener
 * Calling this function will stop using GPS in your app
 * */
public void stopUsingGPS(){
    if(locationManager != null){
        locationManager.removeUpdates(gpsTracker.this);
    }
}

/**
 * Function to get latitude
 * */
public double getLatitude(){
    if(location != null){
        latitude = location.getLatitude();
    }

    // return latitude
    return latitude;
}

/**
 * Function to get longitude
 * */
public double getLongitude(){
    if(location != null){
        longitude = location.getLongitude();
    }

    // return longitude
    return longitude;
}

/**
 * Function to check GPS/wifi enabled
 * @return boolean
 * */
public boolean canGetLocation() {
    return this.canGetLocation;
}

/**
 * Function to show settings alert dialog
 * On pressing Settings button will lauch Settings Options
 * */
public void showSettingsAlert(){
    AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);

    // Setting Dialog Title
    alertDialog.setTitle("GPS is settings");

    // Setting Dialog Message
    alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");

    // On pressing Settings button
    alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog,int which) {
            Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
            mContext.startActivity(intent);
        }
    });

    // on pressing cancel button
    alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
            dialog.cancel();
        }
    });

    // Showing Alert Message
    alertDialog.show();
}

@Override
public void onLocationChanged(Location location) {
}

@Override
public void onProviderDisabled(String provider) {
}

@Override
public void onProviderEnabled(String provider) {
}

@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}

@Override
public IBinder onBind(Intent arg0) {
    return null;
}

Answer 1

From what is specified[difference of 4-5 blocks], you may be obtaining the location from networkProvider only.

With this gpsTracker code mentioned in the question,
there are a few modifications required, instead of using the code as it is:

1. There are 2 if loops which verify the source of location is enabled or not and No 'else':

 if (isNetworkEnabled) {
                locationManager.requestLocationUpdates(
                        LocationManager.NETWORK_PROVIDER,
                        MIN_TIME_BW_UPDATES,
                        MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                Log.d("Network", "Network");
                if (locationManager != null) {
                    location = locationManager
                            .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                    if (location != null) {
                        latitude = location.getLatitude();
                        longitude = location.getLongitude();
                    }
                }
            }
            // if GPS Enabled get lat/long using GPS Services
            if (isGPSEnabled) {
                if (location == null) {
                    locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    Log.d("GPS Enabled", "GPS Enabled");
                    if (locationManager != null) {
                        location = locationManager
                                .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
            }  

This means the application is going to do twice the work when you can obtain the location from both sources. Further, the source of location obtained always remains ambiguous.

This is good when you just need approximate location which should not be null majorly.

If you want to use only this class to obtain location, try structuring the if-else according to requirement and ensuring that its not going to repeat if the location is obtained.
Eg. if GPS is on a higher preference, applies in your case, shift that if above and put the network condition with an else like:

if (isGPSEnabled) {
                if (location == null) {
                    locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    Log.d("GPS Enabled", "GPS Enabled");
                    if (locationManager != null) {
                        location = locationManager
                                .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
            } else if (isNetworkEnabled) {
            locationManager.requestLocationUpdates(
                    LocationManager.NETWORK_PROVIDER,
                    MIN_TIME_BW_UPDATES,
                    MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
            Log.d("Network", "Network");
            if (locationManager != null) {
                location = locationManager
                        .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                if (location != null) {
                    latitude = location.getLatitude();
                    longitude = location.getLongitude();
                }
            }
        }

For your requirement, i suggest removing the network provider part and obtaining the location only from GPS, esp if line of sight is not a problem.

When your code was working fine, it must be fetching the location from GPS and setting it in the object. But because of the two "if" and no "else", you'l never know whether location obtained is from Network or GPS - you can check location.getProvider() inside the condition of canGetLocation()

2. Also, you can log the message or prompt some action for one particular source...like:
In this part:

 if (!isGPSEnabled && !isNetworkEnabled) {
            // no network provider is enabled
        }    

just separate it into two different if(s) and code accordingly. As of now, nothing happens here so you wouldn't know if both are disabled unless you check it externally.

Suggestion: Try the LocationClient which uses GooglePlayServices for Retrieving Current Location . I have found it more reliable and useful. Check this Fused Location Provider example, setting LocationRequest object according to your requirement is the key.

Another update: just came across: useful ques on stack overflow - Good way of getting the users location

---

Update for anybody looking up this question/answer
Regarding the suggestion of LocationClient;
LocationClient is no longer found under com.google.android.gms.location, refer:
Android play services 6.5: LocationClient is missing