22  Getting location updates with OpenStreetMaps

Figure 14-14.

14.22 Getting location updates with OpenStreetMaps | 585



www.it-ebooks.info



Figure 14-15.

586 | Chapter 14: Location and Map Applications



www.it-ebooks.info



Problem

You need to react to the changes in the device's location and move the map focus to

changed location



Solution

Using LocationListener, an application can request for location updates and then react

to these changes in location



Discussion

• The activity that includes the OSM MapView needs to implement "LocationListener" to be able to request for changes in the device's location. An activity implementing LocationListener will also need to add the unimplemented (abstract)

methods from LocationListener interface (Eclipse will do this for you). We set the

center of the map to the GeoPoint named mapCenter so that the application starts

with map focussed around that point.

• Now we need to get an instance of "LocationManager" and use to to request for

location updates using the requestLocationUpdates method.

• One of the overridden methods (which were abstract in the LocationListener interface) named 'onLocationChanged' we can write the code that we want to be

executed when the location of the device changes.

• In the onLocationChanged method we obtain the latitude and longitude of the new

location and set the map's center to the new GeoPoint.

Example 14-64.

public class LocationChange extends Activity implements LocationListener {

private LocationManager myLocationManager;

private MapView mapView;

private MapController mapController;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

mapView = (MapView)findViewById(R.id.mapview);

mapController = this.mapView.getController();

mapController.setZoom(15);

GeoPoint mapCenter = new GeoPoint(53554070, -2959520);

mapController.setCenter(mapCenter);

myLocationManager = (LocationManager) getSystemService(LOCATION_SERVICE);

myLocationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 1000, 100, this);

}

@Override

public void onLocationChanged(Location location) {

int latitude = (int) (location.getLatitude() * 1E6);



14.22 Getting location updates with OpenStreetMaps | 587



www.it-ebooks.info



int longitude = (int) (location.getLongitude() * 1E6);

GeoPoint geopoint = new GeoPoint(latitude, longitude);

mapController.setCenter(geopoint);

mapView.invalidate();

}

@Override

public void onProviderDisabled(String arg0) {

}

@Override

public void onProviderEnabled(String arg0) {

}

@Override

public void onStatusChanged(String arg0, int arg1, Bundle arg2) {

}



}



When the application starts, the map is centered around the mapCenter GeoPoint.

Since the application is listening to location changes, the icon in the top bar of the

phone is visible:

Now using the Emulator controls new GPS coordinates (-122.094095, 37.422006) are

sent to the emulator. The application reacts to it and centers the map around then new

coordinates:

Similarly, different GPS coordinates are given from the Emulator controls and the application centers the map around the new location:

Also, to allow the application to listen for location changes, include these permissions

in the AndroidManifest.

Example 14-65.







android:name="android.permission.ACCESS_COARSE_LOCATION"/>

android:name="android.permission.ACCESS_FINE_LOCATION"/>

android:name="android.permission.ACCESS_NETWORK_STATE" />

android:name="android.permission.INTERNET" />



Source Download URL

The source code for this example may be downloaded from this URL: https://docs.goo

gle.com/leaf?id=0B_rESQKgad5LNGViMzhmM2ItZG

FiZC00NGVhLWJmNjctNTRjNTA0M2QzMjdh&hl=en_US



588 | Chapter 14: Location and Map Applications



www.it-ebooks.info



Figure 14-16.

14.22 Getting location updates with OpenStreetMaps | 589



www.it-ebooks.info



Figure 14-17.

590 | Chapter 14: Location and Map Applications



www.it-ebooks.info



Figure 14-18.



14.22 Getting location updates with OpenStreetMaps | 591



www.it-ebooks.info



Binary Download URL

The executable code for this example may be downloaded from this URL: https://docs

.google.com/leaf?id=0B_rESQKgad5LNDM0NWVlYTUtNjAzNy00ODJjLTkwM

mItNTFhOTFiZjk0ODdk&hl=en_US



592 | Chapter 14: Location and Map Applications



www.it-ebooks.info



CHAPTER 15



Accellerometer



15.1 Using the accelerometer to detect shaking of the device

Thomas Manthey



Problem

Sometimes it makes sense to evaluate not only on-screen input, but also gestures like

tilting or shaking the telephone. But how can you use the accelerometer to detect

whether the phone has been shaken?



Solution

The solution is to register with the accelerometer and to compare the current acceleration values on all three axes to the previous ones. If the values have repeatedly changed

on at least two axises and those changes exceed a high enough threshold, you can clearly

determine shaking.



Discussion

Let us first define shaking as a fairly rapid movement of the device in one direction

followed by further one in another direction, mostly but not necessarily the opposite.

If we want to detect such a shake motion in an activity, we need a connection to the

hardware sensors, those are exposed by the class SensorManager. Furthermore we need

to define a SensorEventListener and register it with the SensorManager.

So the source of our activity starts like this:

Example 15-1.

public class ShakeActivity extends Activity {

/* The connection to the hardware */

private SensorManager mySensorManager;

/* The SensorEventListener lets us wire up to the real hardware events */

private final SensorEventListener mySensorEventListener = new SensorEventListener() {



593



www.it-ebooks.info



public void onSensorChanged(SensorEvent se) {

/* we will fill this one later */

}

public void onAccuracyChanged(Sensor sensor, int accuracy) {

/* can be ignored in this example */

}

};

....



To implement SensorEventListener, we have to implement to methods - onSensorCh

anged(SensorEvent se) and onAccuracyChanged(Sensor sensor, int accuracy). The

first one gets called whenever new sensor data is available, the second one whenever

the accuracy of measurement changes, e.g. when the location service switches from

GPS to network-based. In our example we just need to cover onSensorChanged.

Before we continue, let us define some more variables, which will store the information

about values of acceleration and some state.

Example 15-2.

/* Here we store the current values of acceleration, one for each axis */

private float xAccel;

private float yAccel;

private float zAccel;

/* And here the previous ones */

private float xPreviousAccel;

private float yPreviousAccel;

private float zPreviousAccel;

/* Used to suppress the first shaking */

private boolean firstUpdate = true;

/*What acceleration difference would we assume as a rapid movement? */

private final float shakeThreshold = 1.5f;

/* Has a shaking motion been started (one direction) */

private boolean shakeInitiated = false;



I hope that the names and comments do explain enough about what is stored in these

variables, if not, it will become clearer in the next steps. Now let us connect to the

hardware sensors and wire up for their events, onCreate is the perfect place to do so.

Example 15-3.

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

mySensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE); // (1)

mySensorManager.registerListener(mySensorEventListener, mySensorManager



594 | Chapter 15: Accellerometer



www.it-ebooks.info