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This tutorial describes the usage of the fused location provider.

1. Android Location API

1.1. Determine the current geolocation

Most Android devices allow to determine the current geo location. This can be done via a GPS (Global Positioning System) module, via cell tower triangulation and via wifi networks.

Google Play provides the fused location provider to retrieve the device’s last known location.

1.2. Installation

To use the location manager make the Google play service available via your app build.gradle file.

dependencies {
    compile 'com.google.android.gms:play-services:9.2.0'
    compile 'com.google.android.gms:play-services-location:9.2.0'
    }

Also specify the following required permission in your manifest.

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

1.3. Using the LocationManager

Now you can access the last known location. The fuse location provider provides a new simple API. The following is an example activity which uses it.

1.4. Forward and reverse Geocoding

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. The Geocoder class uses an online Google service.

1.5. Security

If you want to access the GPS sensor, you need the ACCESS_FINE_LOCATION permission. Otherwise you need the ACCESS_COARSE_LOCATION permission.

1.6. Prompt the user to Enabled GPS

The user can decide if the GPS is enabled or not.

You can find out, if a LocationManager is enabled via the isProviderEnabled() method. If its not enabled you can send the user to the settings via an Intent with the Settings.ACTION_LOCATION_SOURCE_SETTINGS action for the android.provider.Settings class.

LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);
boolean enabled = service
    .isProviderEnabled(LocationManager.GPS_PROVIDER);

// check if enabled and if not send user to the GSP settings
// Better solution would be to display a dialog and suggesting to 
// go to the settings
if (!enabled) {
  Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
    startActivity(intent);
}

Typically you would open an AlarmDialog prompt the user and if he wants to enable GPS or if the application should be canceled.

You cannot enable the GPS directly in your code, the user has to do this.

2. Using GPS and setting the current location

2.1. Activating GPS on the emulator

You need to activate GPS on your test device. If you test on the emulator and its not activated you "null" if you try to use a LocationManager.

The Google Map activity should automatically activate the GPS device in the emulator but if you want to use the location manager directly you need to do this yourself. Currently their seems to be an issue with this.

Start Google Maps on the emulator and request the current geo-position, this will allow you to activate the GPS. Send new GPS coordinates to the Android emulator.

2.2. Setting the geoposition

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 the Send button.

You can also 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

3. Tutorial: Using the Android Location API

3.1. Create Project

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

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

Change your layout file from the <filename class="directory">res/layout_ folder to the following code.

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

3.2. Add permissions

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

INTERNET
ACCESS_FINE_LOCATION
ACCESS_COARSE_LOCATION

3.3. Activity

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;

    /** Called when the activity is first created. */
    @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.");
            onLocationChanged(location);
        } else {
            latituteField.setText("Location not available");
            longitudeField.setText("Location 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();
    }
}

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