Introduction to Otto

BusProvider.java

/**
 * BusProvider is a Singleton which provides
 * app-wide access to a single Bus instance.
 */
public class BusProvider
{
 private static BusProvider instance;
 
 public BusProvider getInstance()
 {
  if(instance == null)
   instance = new BusProvider();
  
  return instance;
 }
 
 private Bus bus;
 
 private BusProvider()
 {
  bus = new Bus(ThreadEnforcer.ANY)
 }
 
 public Bus getBus()
 {
  return bus;
 }
}

LocationEvent.java

/**
 * An event object that encapsulates the location
 * data we care about broadcasting.
 */
public class LocationEvent
{
 private LatLng location;
 
 public LocationEvent(LatLng location)
 {
  this.location = location;
 }
 
 public LatLng getLocation()
 {
  return location;
 }
}

LocationService.java

/**
 * Pretend that this LocationService is an Android
 * Service running in the background tracking changes
 * in the user's location.
 */ 
public class LocationService extends Service
{
 private Bus bus;
 
 public void onCreate()
 {
  super.onCreate();
  
  bus = BusProvider.getInstance().getBus();
 }
 
 // ... implement all the service methods needed
 
 // ... implement location tracking behavior
 
 // broadcasts new user locations to anyone who cares
 private void broadcastNewLocation(LatLng location)
 {
  LocationEvent event = new LocationEvent(location);
  bus.post( event );
 }
}

MyActivity.java

pulic class MyActivity extends Activity
{
 private Bus bus;
 
 @Override
 public void onCreate(Bundle savedInstanceState)
 {
  super.onCreate(savedInstanceState);
  bus = BusProvider.getInstance().getBus();
 }
 
 @Override
 public void onStart()
 {
  super.onStart();
  
  // start listening for events
  bus.register(this);
 }
 
 @Override
 public void onStop()
 {
  super.onStop();
  
  // stop listening for events
  bus.unregister(this);
 }
 
 @Subscribe
 public void onLocationChange(LocationEvent event)
 {
  LatLng newLocation = event.getLocation();
  
  // do whatever you want with the user's new location
  
  // it doesn't get any easier than this to monitor a
  // user's location in an Activity/Fragment
 }
}