Updating Activity TextView from service using Serv

Question

I have a service for reading GPS latitude and longitude. I would like to update the activity from the service's locationlistener's onLocationChanged.

How can I achieve it? I have been reading on Service Bound but it looks like it is only for activity to invoke the methods in service but not service invoke textView in Activity. Is binding service is not possible to achieve it?

Answer 1

What stops you from declaring a method like this (in your service):

public void setTextViewToModify(TextView tv);

After you gave the reference of the TextView to your Service, it can access it just like any other object.

In the other hand, I do not suggest this solution, because this way it is really easy to cause memory leaks. Also, the TextView should not leave the Activity's context since it is a part of the Activity. The reference would remain in the Service, even after the Activity is destroyed, and I guess you can imagine what would happen if the Service touched the dead TextView.

You should broadcast the updates from your service, and use a LocalBroadcastRecever to get those updates in your Activity. That way the TextView will be updated by the one who is responsible for that, the Activity itself.

If you don't like the concept of LocalBroadcatReceiver you can try any of the event bus solutions. It is more easy to use, and you can pass any kind of objects. You do not have to make them marshallable (Serializable/Parcelable).

• http://square.github.io/otto/
• https://github.com/greenrobot/EventBus

Answer 2

You should use the LocalBroadcastManager class from within your Service to send an Intent back to the Activity.

For Example, An Activity containing a single TextView can set up a BroadcastReceiver like such:

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final TextView textView = (TextView) findViewById(R.id.main_activity_text_view);

        LocalBroadcastManager.getInstance(this).registerReceiver(
                new BroadcastReceiver() {
                    @Override
                    public void onReceive(Context context, Intent intent) {
                        double latitude = intent.getDoubleExtra(LocationBroadcastService.EXTRA_LATITUDE, 0);
                        double longitude = intent.getDoubleExtra(LocationBroadcastService.EXTRA_LONGITUDE, 0);
                        textView.setText("Lat: " + latitude + ", Lng: " + longitude);
                    }
                }, new IntentFilter(LocationBroadcastService.ACTION_LOCATION_BROADCAST)
        );
    }

    @Override
    protected void onResume() {
        super.onResume();
        startService(new Intent(this, LocationBroadcastService.class));
    }

    @Override
    protected void onPause() {
        super.onPause();
        stopService(new Intent(this, LocationBroadcastService.class));
    }
}

And a basic Service can broadcast all location changes as follows:

public class LocationBroadcastService extends Service {

    public static final String
            ACTION_LOCATION_BROADCAST = LocationBroadcastService.class.getName() + "LocationBroadcast",
            EXTRA_LATITUDE = "extra_latitude",
            EXTRA_LONGITUDE = "extra_longitude";

    private static final int
            MIN_TIME = 2000,
            MIN_DISTANCE = 1;

    @Override
    public void onCreate() {
        super.onCreate();
        LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        sendBroadcastMessage(locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER));
        locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, MIN_TIME, MIN_DISTANCE,
                new LocationListener() {
                    @Override
                    public void onLocationChanged(Location location) {
                        sendBroadcastMessage(location);
                    }

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

                    }

                    @Override
                    public void onProviderEnabled(String provider) {

                    }

                    @Override
                    public void onProviderDisabled(String provider) {

                    }
                }
        );
    }

    private void sendBroadcastMessage(Location location) {
        if (location != null) {
            Intent intent = new Intent(ACTION_LOCATION_BROADCAST);
            intent.putExtra(EXTRA_LATITUDE, location.getLatitude());
            intent.putExtra(EXTRA_LONGITUDE, location.getLongitude());
            LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
        }
    }


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