Location Manager | Android Developer Tutorial (Part 15)

Location-based service is another key functionality that gets used by mobile applications. IT is often combined with maps to give a good user experience. We have already see how to use the external Google Maps API in tutorial Part 14. Here I will build upon the same to show how changes in location can be displayed on the map.

The location services are provided in the android.location package.

In order to use location services, our activity needs to implement the LocationManager Interface.

What does a LocationManager provide?

It is through this interface that an application can access the system’s location services. These services basically allow the application to obtain periodic updates of the device’s geographical location. It also helps in firing an application specific intent when the device comes within the proximity of a specified location.

Since in my example I want to simulate a location change and make my activity respond to the same, I am implementing this interface.

In order to make it an effective application, I have shown my location (hard-coded) on the google map. Then, I have used the location manager to handle any change in the location. The change in location needs to be simulated on the emulator by connecting through telnet. How to simulate location change is given at the end of this tutorial.

Now, dive into the code.

NOTE: I am adding the LocationManager implementation to the same MapActivity class created in the earlier tutorial (Part 14) and hence will not be explaining anything related to the maps API here.

Step 1: Obtain the LocationManager instance:

LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 1000L, 500.0f, this);

After getting the location manager, I am setting default GPS provider and asking to be notified if the location changes by more than 500 meters from the current location, the frequency of updation being 1 sec.

Step 2: Override the onLocationChanged() method in order to respond to changes in location.

      public void onLocationChanged(Location location) {

            if (location != null) {

                  double lat = location.getLatitude();

                  double lng = location.getLongitude();

                  String currentLocation = "The location is changed to Lat: " + lat + " Lng: " + lng;

                  myLoc.setText(currentLocation);

                  geoPoint = new GeoPoint((int) lat * 1000000, (int) lng * 1000000);

                  myMC.animateTo(geoPoint);

            }

      }

This method gets invoked when we change the location through the telnet connection to the emulator as described at the end of the tutorial. Based on the latitude and the longitude settings sent, the GeoPoint is changed to display the new location.

That is it. I have not overridden any of the other methods provided by the locationManager. Complete code is downloadable here.

How to simulate location change in the emulator?

Start the Emulator from eclipse

Start a command prompt

Start telnet

Then, type, o localhost 5554

This connects the telnet client to the android emulator (assuming emulator is running locally listening on port 5554. Else this connection fails)

Now type

geo fix 79.000000 13.000000 (or your latitude and longitude)

This sends the location change signal to the emulator.