无法获得经纬度和长时间使用GPS提供程序

Question

ReminderLogic service class invokes GPSTracker Service class. isGPSEnabled is true. GPS was on in the device and was clearly under sky view. Still the lat and long is 0.0.

location = locationManager
                                .getLastKnownLocation(Context.LOCATION_SERVICE);

and

location = locationManager
                                .getLastKnownLocation(LocationManager.GPS_PROVIDER);

gives location as null.

Could someone please help me.

//ReminderLogic Service Class

            GPSTracker gps;
        double CurrLatitude, CurrLongitude;
        Location CurrentLoc;
        gps = new GPSTracker(HomePageActivity.this); 
if (gps.canGetLocation()) {
                CurrLatitude = gps.getLatitude();
                CurrLongitude = gps.getLongitude();

                Toast.makeText(
                        getApplicationContext(),
                        "canGetLocation is True. CurrLatitude and CurrLongitude is "
                                + CurrLatitude + CurrLongitude, Toast.LENGTH_LONG)
                        .show();
            }

//GPS Tracker Service class

          if (isGPSEnabled) {

                this.canGetLocation = true;
                if (location == null) {
                    locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER, 0, 0, this);
                    Log.d("GPS Enabled", "GPS Enabled");
                    if (locationManager != null) {
                        location = locationManager
                                .getLastKnownLocation(Context.LOCATION_SERVICE);
                        location = locationManager
                                .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
            }

Answer 1

try to override onLocationChanges(Location location)

      @Override
     public void onLocationChanged(Location location) {
    if (location != null)
    {
        Log.i("SuperMap", "Location changed : Lat: " + location.getLatitude() + " Lng: " + location.getLongitude());
        latitude = location.getLatitude();
        longitude = location.getLongitude();
        Log.i("latitude,longitude", ""+latitude+","+longitude);


    } 
}

Answer 2

First of all I will explain your that why your code is not working.

You are using GPS to get the location which takes some time to get your location and on getting the location fires onLocationChanged Listener.

However, in your code you are asking GPS to get your location using

locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER, 0, 0, this);

and then expecting it to give you location in a second. You need a LocationListener to listen to the location when GPS tracks you. This may take upto 20 minutes and depends on whether the GPS has a direct access to a satellite eg. if your device is inside a building, GPS will take several minutes to track you but if you in open the GPS will track you fast.

To use LocationListener just add implements LocationListener in your class declaration. Then in onLocationChanged() use the following to get your location.

@Override
     public void onLocationChanged(Location location) {
    if (location != null)
    {
       Log.d("Location Found", location.getLatitude() + " " + location.getLongitude());
    locationManager.removeUpdates(this);
    } 
}

locationManager.removeUpdates(this); stops android from sending you locations endlessly and is important.

Also you can the LocationListener Class internally by using

LocationListener locationListener = new LocationListener() {
        @Override
        public void onLocationChanged(Location location) {
              Log.d("Location Found", location.getLatitude() + " " + location.getLongitude());
    locationManager.removeUpdates(this);
        }

        @Override
        public void onStatusChanged(String s, int i, Bundle bundle) {

        }

        @Override
        public void onProviderEnabled(String s) {

        }

        @Override
        public void onProviderDisabled(String s) {

        }
    }

But you must update the requestLocationUpdates() like this

locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER, 0, 0, locationListener);

Update:-

You are checking if your locationManager is not null after requestLocationUpdates() which won't be null since you initialized it. Then you are using

location = locationManager
                                .getLastKnownLocation(Context.LOCATION_SERVICE);

to get the last Known Location which will only be present if you have earlier used any app to get a location. eg. if you use Google Maps app to get your location, then after Google Maps detect your position, you open your own app then you will get LastKnownLocation . This is due to the fact that android has your position from the past.

If you never got any location previously, then you won't get any result from it. Besides, this is the wrong way of coding. You should do like this

location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
}
else{
locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER, 0, 0, this);
}

This way, if you have a previous location you can use it, if not, then you get a new one.

Answer 3

Change your code as:

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
if (locationManager != null) {
    location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
    if (location != null) {
        latitude = location.getLatitude();
        longitude = location.getLongitude();
    }
}

Hope this helps.