Location Based Services
- Android gives our applications access to the location services through the classes in the android.location package.
- We can utilize GPS and Android’s Network Location Provider to acquire the user location.
- GPS provider:
- GPS is most accurate.
- It works only outdoors.
- Quickly consumes battery power.
- Doesn't return the location as quickly as user want.
- Network Location Provider:
- Determines the user location using the cell-tower and Wi-Fi signals.
- It works indoors and outdoors.
- Responds faster.
- It uses less battery.
- To obtain the user location we can use both GPS and Network Location Provider or just one.
- Key classes:
- LocationManager.
- LocationProvider.
- LcoationManager provides access to the system location services. This is done through getSystemService.
- Using LocationManager class we can obtain periodic updates of the locations.
- We can request location updates of devices using requestLocationUpdates() method. This method takes four parameters:
- Provider - The name of the location provider you wish to use.
- minTime - The minimum time interval for notifications, in milliseconds.
- minDistance - The minimum distance interval for notifications, in meters.
- listener - An object whose onLocationChanged() method will be called for each location update.
- In order to receive location updates we must request user permissions.
- NETWORK_PROVIDER – android.permission.ACCESS_COARSE_LOCATION.
- GPS_PROVIDER - android.permission.ACCESS_FINE_LOCATION.
- The following statement should be added to the AndroidManifest.xml
- < uses-permission android:name=”android.permission.ACCESS_FINE_LOCATION” />
- If we are using both
NETWORK_PROVIDER and GPS_PROVIDER, then we need to request only the ACCESS_FINE_LOCATION permission, because it includes permission for both providers.
- Using DDMS we can simulate location data in several ways through Emulator Controls. They are as follows:
- Manually send individual longitude/latitude coordinates to the device.
- Use a GPX file describing a route for playback to the device.
- Use a KML file describing individual place marks for sequenced playback to the device.
- To send location data through DDMS we must be sure that a device selected in the Devices panel. (Available from Window > Show View > Other > Devices).
Ø Example:
Main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello"
/>
<Button
android:id="@+id/retrieve_location_button"
android:text="Get Location"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</LinearLayout>
GeoCoderActivity.java:
package com.snigdha.android;
import android.app.Activity;
import android.content.Context;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;
public class GeoCoderExampleActivity extends Activity {
/** Called when the activity is first created. */
private static final long MINIMUM_DISTANCE_CHANGE_FOR_UPDATES = 1;
private static final long MINIMUM_TIME_BETWEEN_UPDATES = 1000;
protected LocationManager locationManager;
protected Button retrieveLocationButton;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
retrieveLocationButton = (Button) findViewById(R.id.retrieve_location_button);
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
locationManager.requestLocationUpdates( LocationManager.GPS_PROVIDER, MINIMUM_TIME_BETWEEN_UPDATES,MINIMUM_DISTANCE_CHANGE_FOR_UPDATES,
new MyLocationListener() );
retrieveLocationButton.setOnClickListener(new OnClickListener() {
public void onClick(View v) { showCurrentLocation();
}
});
}
protected void showCurrentLocation() {
Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location != null) {
String message = String.format( "Current Location \n Longitude: %1$s \n Latitude: %2$s", location.getLongitude(), location.getLatitude() );
Toast.makeText(GeoCoderExampleActivity.this, message, Toast.LENGTH_LONG).show();
}
}
private class MyLocationListener implements LocationListener {
public void onLocationChanged(Location location) {
String message = String.format( "New Location \n Longitude: %1$s \n Latitude: 2$s", location.getLongitude(), location.getLatitude() );
Toast.makeText(GeoCoderExampleActivity.this, message, oast.LENGTH_LONG).show();
}
public void onStatusChanged(String s, int i, Bundle b) {
Toast.makeText(GeoCoderExampleActivity.this, "Provider status changed",
Toast.LENGTH_LONG).show();
}
public void onProviderDisabled(String s) {
Toast.makeText(GeoCoderExampleActivity.this, "Provider disabled by the user. GPS turned off", Toast.LENGTH_LONG).show();
}
public void onProviderEnabled(String s) { Toast.makeText(GeoCoderExampleActivity.this, "Provider enabled by the user. GPS turned on", Toast.LENGTH_LONG).show();
}
}
}
AndroidManifest.xml:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.snigdha.android"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" />
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_MOCK_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".GeoCoderExampleActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
Screen Shots:
 |
| Figure-1 |
 |
| Figure - 2 |
 |
| Figure - 4 |
 |
| Figure - 3 |
- Figure-2 displaying the current location data retrieved by the provider.
- Figure-3 and Figure -4 showing a toast messages when the GPS is disabled and enabled by the user.
The screen has turned off.
