Question

i have a LocationService class (extends Service implements LocationListener) that works constantly updates a global variable whenever a new location is obtained via the onLocationChanged method.

in the onCreate method of my launcher activity, i start this service. the next thing i do is to call a web service that takes in the latitude and longitude from the global variable.

this gives me a NullPointerException on the location global variable and i am assuming its because the service is running on a separate thread and have not obtained a location yet.

Question: how do i make it such that i will only call the web service only when a location has been obtained from the service class?

thanks so much. 🙂

Answer 1

YourService informs every registered LocationOperator when location is changed. LocationOperator is a simple interface, declares operate(Location) method.

class YourService extends Service implements LocationListener {
    private List<LocationOperator> listeners = new ArrayList<LocationOperator>();

    public List<LocationOperator> getListeners() {
            return listeners;
    }

    @Override
    public void onLocationChanged(Location location) {
            for (LocationOperator listener : listeners) {
                    listener.operate(location);
            }
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
            // request location updates from `LOCATION_SERVICE`
            return Service.START_NOT_STICKY;
    }

    //...
}

Start and connect to this service from your main activity

public class MainActivity extends Activity {

    static YourService yourService;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        //...
        Intent service = new Intent(this, YourService.class);
        startService(service);
        bindService();
    }

    // ...
}

Then you can reach this service over MainActivity and register for Location

public class OperatorActivity extends Activity implements LocationOperator {

    @Override
    public void onCreate(Bundle instance) {
        // ...
        MainActivity.yourService.getListeners().add(this);
        // ...
    }

    public void operate(Location location) {
        // use location
    }
}