Zeeshan Akhter

Most Android devices allow to determine the current geolocation. This can be done via a GPS (Global Positioning System) device, via cell tower triangulation or via wifi networks for which the geolocation is known. Android contains the android.location package which provides the API to determine the current geo position.

The LocationManager provides access to the Android location service. This services allows to access location providers, to register location update listeners and proximity alerts and more.

The LocationProvider class provides location data via the Location class. The LocationProvider class is the superclass of the different location providers which deliver the information about the current location.

The Android device might have several LocationProvider available and you can select one of them. For a flexible selection of the best location provider use a Criteria object in which you can define how the provider should be selected.

You can register a LocationListener object with the LocationManager class to receive periodic updates about the geoposition.

You can also register an Intent which allows to define a proximity alert, this alert will be triggered if the device enters a area given by a longitude, latitude and radius (proximity alert).

The Geocoder class allows to determine the geo-coordinates (longitude, laditude) for a given address and possible addresses for given geo-coordinates.

This process is known as forward and reverse geocoding.

If you want to access the GSP then you need the ACCESS_FINE_LOCATION permission. Otherwise you need the ACCESS_COARSE_LOCATION.

You can use the “DDMS” Perspective of Eclipse to send your geoposition to the emulator or a connected device. For open this Perspective select Window → Open Perspective → Other → DDMS.

In the Emulator Control part you can enter the geocoordinates and press “Send.”

You can als set the geoposition the Android emulator via telnet. Open a console and connect to your device. The port number of your device can be seen in the title area of your emulator.

				
telnet localhost 5554

Set the position via the following command.

				
geo fix 13.24 52.31

Create a new project called “de.vogella.android.locationapi.simple” with the Activity called “ShowLocationActivity”.

This example will not use the Google Map therefore is also runs on an Android device.

Change your “main.xml” layout file from the “res/layout” folder to the following:

				
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <LinearLayout
        android:id="@+id/linearLayout1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="40dip"
        android:orientation="horizontal" >

        <TextView
            android:id="@+id/TextView01"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="10dip"
            android:layout_marginRight="5dip"
            android:text="Latitude: "
            android:textSize="20dip" >
        </TextView>

        <TextView
            android:id="@+id/TextView02"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="unknown"
            android:textSize="20dip" >
        </TextView>
    </LinearLayout>

    <LinearLayout
        android:id="@+id/linearLayout2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <TextView
            android:id="@+id/TextView03"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="10dip"
            android:layout_marginRight="5dip"
            android:text="Longitute: "
            android:textSize="20dip" >
        </TextView>

        <TextView
            android:id="@+id/TextView04"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="unknown"
            android:textSize="20dip" >
        </TextView>
    </LinearLayout>

</LinearLayout>

Add the following permissions to your application in your “AndroidManifest.xml” file

Change ShowLocationActivity to the following. It queries the location manager and display the queried values in the activity.

package de.vogella.android.locationsapi.simple;

import android.app.Activity;
import android.content.Context;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.widget.TextView;
import android.widget.Toast;

public class ShowLocationActivity extends Activity implements LocationListener {
	private TextView latituteField;
	private TextView longitudeField;
	private LocationManager locationManager;
	private String provider;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		latituteField = (TextView) findViewById(R.id.TextView02);
		longitudeField = (TextView) findViewById(R.id.TextView04);

		// Get the location manager
		locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
		// Define the criteria how to select the locatioin provider -> use
		// default
		Criteria criteria = new Criteria();
		provider = locationManager.getBestProvider(criteria, false);
		Location location = locationManager.getLastKnownLocation(provider);

		// Initialize the location fields
		if (location != null) {
			System.out.println("Provider " + provider + " has been selected.");
			int lat = (int) (location.getLatitude());
			int lng = (int) (location.getLongitude());
			latituteField.setText(String.valueOf(lat));
			longitudeField.setText(String.valueOf(lng));
		} else {
			latituteField.setText("Provider not available");
			longitudeField.setText("Provider not available");
		}
	}

	/* Request updates at startup */
	@Override
	protected void onResume() {
		super.onResume();
		locationManager.requestLocationUpdates(provider, 400, 1, this);
	}

	/* Remove the locationlistener updates when Activity is paused */
	@Override
	protected void onPause() {
		super.onPause();
		locationManager.removeUpdates(this);
	}

	@Override
	public void onLocationChanged(Location location) {
		int lat = (int) (location.getLatitude());
		int lng = (int) (location.getLongitude());
		latituteField.setText(String.valueOf(lat));
		longitudeField.setText(String.valueOf(lng));
	}

	@Override
	public void onStatusChanged(String provider, int status, Bundle extras) {
		// TODO Auto-generated method stub

	}

	@Override
	public void onProviderEnabled(String provider) {
		Toast.makeText(this, "Enabled new provider " + provider,
				Toast.LENGTH_SHORT).show();

	}

	@Override
	public void onProviderDisabled(String provider) {
		Toast.makeText(this, "Disabled provider " + provider,
				Toast.LENGTH_SHORT).show();
	}
}

If you using the emulator send some geo-coordinates to your device. These geo-coordinate should be displayed as soon as you press the button.

Google provides via the com.google.android.maps package a library for using the MapView in your application. You require an additional key to use them. This key will be specified in the View which displays the map.

You need to add the following uses-library statement to your AndroidManifest.xml file. The project creation wizard does this automatically if you select a Google API version.

				
<uses-library android:required="true" android:name="com.google.android.maps"></uses-library>

The usage of MapView requires the permission to access the Internet, as the data displayed in the MapView is downloaded from the Internet.

The MapActivity class extends the Activity class and provides the life-cycle management and the services for displaying a MapView widget.

MapActivity simplify the handling MapViews similar to ListActivity simplifies the usage of ListViews.

A MapView is typically defined in the XML layout file used by the MapActivity and requires the API key in the “android:apiKey” attribute. A MapView can be used with other user interface components in the same layout.

The MapController class can be used to interact with the MapView, e.g. by moving it. A Geopoint is a position described via latitude and longitude.

You can also draw OverlayItem on the map. These are typical graphics which you want to display on the map.

You must declare that your application uses the com.google.android.maps library in the application of your AndroidManifest.xml file. Please note that the usage declaration must be in the application tag otherwise you get java.lang.ClassNotFoundException for your Activity.

				
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="de.vogella.android.locationapi.maps"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="15" />

    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <uses-library android:name="com.google.android.maps" >
        </uses-library>

        <activity
            android:name="MapViewDemo"
            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>

Create a new Android project called “de.vogella.android.locationapi.maps” with an Activity called “ShowMapActivity”. Make sure to select the “Google API” als Target.

Add the following permissions to your application.

You need to add the Google maps library to your application. Add “uses library” to “AndroidManifest.xml”.

				
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="de.vogella.android.locationapi.maps"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="15" />

    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <uses-library android:name="com.google.android.maps" >
        </uses-library>

        <activity
            android:name="MapViewDemo"
            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>

Create the following class. We will later use an image called “point”. But one icon with this name in your drawable folders.

				
package de.vogella.android.locationapi.maps;

import android.graphics.drawable.Drawable;

import com.google.android.maps.ItemizedOverlay;
import com.google.android.maps.OverlayItem;

public class MyOverlays extends ItemizedOverlay<OverlayItem> {

	private static int maxNum = 3;
	private OverlayItem overlays[] = new OverlayItem[maxNum];
	private int index = 0;
	private boolean full = false;
	private MyOverlays itemizedoverlay;

	public MyOverlays(Drawable defaultMarker) {
		super(boundCenterBottom(defaultMarker));
	}

	@Override
	protected OverlayItem createItem(int i) {
		return overlays[i];
	}

	@Override
	public int size() {
		if (full) {
			return overlays.length;
		} else {
			return index;
		}

	}

	public void addOverlay(OverlayItem overlay) {
		if (index < maxNum) {
			overlays[index] = overlay;
		} else {
			index = 0;
			full = true;
			overlays[index] = overlay;
		}
		index++;
		populate();
	}

}

The next step requires that you have created a valid key for using the MapView widget.

Change the “main.xml” layout file in your “res/layout” folder to the following. and replace “Your Maps API Key” with your Google Maps API key.

				
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/mainlayout"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <com.google.android.maps.MapView
        android:id="@+id/mapview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:apiKey="Your Maps API Key"
        android:clickable="true" />

</RelativeLayout>

Change your Activity to the following. This Activity use an LocationListner to update the MapView with the current location.

				
package de.vogella.android.locationapi.maps;

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.widget.LinearLayout;

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapActivity;
import com.google.android.maps.MapController;
import com.google.android.maps.MapView;
import com.google.android.maps.OverlayItem;

public class ShowMapActivity extends MapActivity {

	private MapController mapController;
	private MapView mapView;
	private LocationManager locationManager;
	private MyOverlays itemizedoverlay;

	public void onCreate(Bundle bundle) {
		super.onCreate(bundle);
		setContentView(R.layout.main); // bind the layout to the activity

		// create a map view
		LinearLayout linearLayout = (LinearLayout) findViewById(R.id.main);
		mapView = (MapView) findViewById(R.id.mapview);
		mapView.setBuiltInZoomControls(true);
		mapView.setStreetView(true);
		mapController = mapView.getController();
		mapController.setZoom(14); // Zoon 1 is world view
		locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
		locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0,
				0, new GeoUpdateHandler());

		Drawable drawable = this.getResources().getDrawable(R.drawable.point);
		itemizedoverlay = new MyOverlays(drawable);
		createMarker();
	}

	@Override
	protected boolean isRouteDisplayed() {
		return false;
	}

	public class GeoUpdateHandler implements LocationListener {

		@Override
		public void onLocationChanged(Location location) {
			int lat = (int) (location.getLatitude() * 1E6);
			int lng = (int) (location.getLongitude() * 1E6);
			GeoPoint point = new GeoPoint(lat, lng);
			createMarker();
			mapController.animateTo(point); // mapController.setCenter(point);

		}		@Override
		public void onProviderDisabled(String provider) {
		}		@Override
		public void onProviderEnabled(String provider) {
		}		@Override
		public void onStatusChanged(String provider, int status, Bundle extras) {
		}
	}	private void createMarker() {
		GeoPoint p = mapView.getMapCenter();
		OverlayItem overlayitem = new OverlayItem(p, "", "");
		itemizedoverlay.addOverlay(overlayitem);
		mapView.getOverlays().add(itemizedoverlay);
	}
}

Run and test your application. You should be able to zoom in and out and send new geocoordinates to your map via the Emulator .

It will also draw Overlays on the Map.