Set up a map activity and create an overlay to show where you are in relation to your friends

Half of the fun in having location sensitive information is drawing it on a map. Create a new activity class to display a map centered on our current location with markers at our friends locations. While we're at it we can draw a line from our position to each of our friends.
The map control itself is called a MapView, but we can only use aMapView in a MapActivity, so we'll change the inheritance of this activity to MapActivity.

public class MyMapViewActivity extends MapActivity

To display the map we need to create a new MapView and set it as the content for our activity in the OnCreate method.

MapView mapView = new MapView(this); setContentView(mapView);

This will make the MapView fill the entire screen, so use views likeLinearLayout if we want to create a more complicated UI layout.
We'll want to get access to the OverlayController and MapController, so create global variables to store them and assign the references within the OnCreate method. We'll also be using the Locationinformation, so get a reference to that too. With the references assigned set your map zoom and starting location using theMapController. When you're finished OnCreate should look something like this.

protected void onCreate(Bundle icicle) {
super.onCreate(icicle); MapView mapView = new MapView(this); mapController = mapView.getController(); overlayController = mapView.createOverlayController(); locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE); mapController.zoomTo(9); setContentView(mMapView); updateView();
}

updateView is where we do the work. Start by getting our current location and convert the Lat/Long to a map Point, then centre the map on our current location.

Double lat = location.getLatitude()*1E6; Double lng = location.getLongitude()*1E6; Point point = new Point(lat.intValue(), lng.intValue()); mapController.centerMapTo(point, false);

The only thing left to do on our map is draw markers and link them up with lines. To do this you need to create a new class that extends Overlay, and add this using the OverlayController.

MyLocationOverlay myLocationOverlay = new MyLocationOverlay(); overlayController.add(myLocationOverlay, true);

The work in the Overlay class is done by overriding the draw method.

protected class MyLocationOverlay extends Overlay {
@Override public void draw(Canvas canvas, PixelCalculator calculator, boolean shadow) {
... [ draw things here ] ...
}
}

I start by drawing a 'marker' on my current location. There doesn't seem to be support for 'traditional' Google Maps markers but you can achieve the same thing by drawing on the map canvas; I chose to draw small circles as markers. First you need to use thePixelCalculator to convert your Lat/Long points to screen coordinates, then create a Paint object to define the colours and settings for your brush. Then paint your markers.

int[] screenCoords = new int[2]; calculator.getPointXY(point, screenCoords); RectF oval = new RectF(...); Paint paint = new Paint(); paint.setARGB(200, 255, 0, 0); canvas.drawOval(oval, paint);

I add my friends locations the same way as before, iterating over my address book grabbing names and locations. I filter out anyone too far away (say 10km) and draw markers, names (drawText), and joining lines (drawLine) to those nearby.