docs/html/training/articles/wear-location-detection.jd

page.title=Detecting Location on Android Wear
page.tags="gps"

page.article=true
@jd:body

<div id="tb-wrapper">
<div id="tb">
<h2>In this document</h2>
<ol class="nolist">
  <li><a href="#Connect">Connect to Google Play Services</a></li>
  <li><a href="#Request">Request Location Updates</a></li>
  <li><a href="#DetectGPS">Detect On-Board GPS</a></li>
  <li><a href="#Disconnection">Handle Disconnection Events</a></li>
  <li><a href="#Notify">Handle Location Not Found</a></li>
  <li><a href="#Synchronize">Synchronize Data</a></li>
</ol>
<!-- Required platform, tools, add-ons, devices, knowledge, etc. -->
<h2>Dependencies and prerequisites</h2>
<ul>
  <li>Android 4.3 (API Level 18) or higher on the handset device</li>
  <li><a href="{@docRoot}google/play-services/index.html">Google Play services</a> 6.1 or higher</li>
  <li>An Android Wear device</li>
</ul>
<h2>See also</h2>
<ul>
  <li><a href="{@docRoot}training/location/index.html">Making Your App Location-Aware
  </a></li>
</ul>
</div></div>

<p>Location awareness on wearable devices enables you to create apps that give users a better
understanding of their geographic position, movement and what's around them. With the small form
factor and glanceable nature of a wearable device, you can build low-friction apps that record and
respond to location data.</p>

<p>Some wearable devices include a GPS sensor that can retrieve location data without another
tethered device. However, when you request location data in a wearable app, you don't have to worry
about where the location data originates; the system retrieves the location updates using the most
power-efficient method. Your app should be able to handle loss of location data, in case the wear
device loses connection with its paired device and does not have a built-in GPS sensor.</p>

<p>This document shows you how to check for on-device location sensors, receive location data, and
monitor tethered data connections.</p>

<p class="note"><b>Note:</b> The article assumes that you know how to use the Google Play services
API to retrieve location data. For more information, see <a href="{@docRoot}training/
location/index.html">Making Your App Location-Aware</a>.</p>

<h2 id="Connect">Connect to Google Play Services</h2>

<p>Location data on wearable devices is obtained though the Google Play services location APIs. You
use the <a href="{@docRoot}reference/com/google/android/gms/location/FusedLocationProviderApi.html">
<code>FusedLocationProviderApi</code></a> and its accompanying classes to obtain this data.
To access location services, create an instance of
<a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.html">
<code>GoogleApiClient</code></a>, which is
the main entry point for any of the Google Play services APIs.
</p>

<p class="caution"><b>Caution:</b> Do not use the existing <a href="{@docRoot}reference/android/location/package-summary.html">Location</a>
APIs in the Android framework. The best practice for retrieving location updates is through the
Google Play services API as outlined in this article.</p>

<p>To connect to Google Play services, configure your app to create an instance of
<a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.html">
<code>GoogleApiClient</code></a>:</p>

<ol>
  <li>Create an activity that specifies an implementation for the interfaces <a
href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.ConnectionCallbacks.html"
>{@code ConnectionCallbacks}</a>, <a href="{@docRoot}reference/com/google/android/gms/common/api/
GoogleApiClient.OnConnectionFailedListener.html">{@code OnConnectionFailedListener}</a>, and <a
href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html">{@code
LocationListener}</a>.</li>
  <li>In your activity's {@link android.app.Activity#onCreate onCreate()} method, create an instance
of <a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.html"><code>
GoogleApiClient</code></a> and add the Location service.
  </li>
  <li>To gracefully manage the lifecycle of the connection, call  <a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.html#connect()">
  {@code connect()}</a> in the {@link android.app.Activity#onResume onResume()} method and
  <a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.html#disconnect()">
  {@code disconnect()}</a> in the {@link android.app.Activity#onPause onPause()} method.
  </li>
</ol>

<p>The following code example shows an implementation of an activity that implements the
<a href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html">
{@code LocationListener}</a> interface:</p>

<pre>
public class WearableMainActivity extends Activity implements
    GoogleApiClient.ConnectionCallbacks,
    GoogleApiClient.OnConnectionFailedListener,
    LocationListener {

    private GoogleApiClient mGoogleApiClient;
    ...

    &#64;Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ...
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addApi(LocationServices.API)
                .addApi(Wearable.API)  // used for data layer API
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .build();
    }

    &#64;Override
    protected void onResume() {
        super.onResume();
        mGoogleApiClient.connect();
        ...
    }

    &#64;Override
    protected void onPause() {
        super.onPause();
        ...
        mGoogleApiClient.disconnect();
    }
}
</pre>

<p>For more information on connecting to Google Play services, see <a href="{@docRoot}google/auth
/api-client.html">Accessing Google APIs</a>.</p>

<h2 id="Request">Request Location Updates</h2>

<p>After your app has connected to the Google Play services API, it is ready to start receiving
location updates. When the system invokes the
<a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.ConnectionCallbacks.html#onConnected(android.os.Bundle)">
<code>onConnected()</code></a> callback for your client, you build the location data request as
follows:</p>

<ol>
  <li>Create a <a
href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html"
>{@code LocationRequest}</a> object and set any options using methods like <a
href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setPriority(int)"
>{@code setPriority()}</a>.
  </li>
  <li>Request location updates using <a href="{@docRoot}reference/com/google/android/gms/location/FusedLocationProviderApi.html#requestLocationUpdates(com.google.android.gms.common.api.GoogleApiClient, com.google.android.gms.location.LocationRequest, com.google.android.gms.location.LocationListener)">
  <code>requestLocationUpdates()</code></a>.
  </li>
  <li>Remove location updates using <a href="{@docRoot}reference/com/google/android/gms/location/FusedLocationProviderApi.html#removeLocationUpdates(com.google.android.gms.common.api.GoogleApiClient, com.google.android.gms.location.LocationListener)">
  <code>removeLocationUpdates()</code></a> in the {@link android.app.Activity#onPause
  onPause()} method.
  </li>
</ol>

<p>The following example shows how to retrieve and remove location updates:</p>

<pre>
&#64;Override
public void onConnected(Bundle bundle) {
    LocationRequest locationRequest = LocationRequest.create()
            .setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY)
            .setInterval(UPDATE_INTERVAL_MS)
            .setFastestInterval(FASTEST_INTERVAL_MS);

    LocationServices.FusedLocationApi
            .requestLocationUpdates(mGoogleApiClient, locationRequest, this)
            .setResultCallback(new ResultCallback<Status>() {

                &#64;Override
                public void onResult(Status status) {
                    if (status.getStatus().isSuccess()) {
                        if (Log.isLoggable(TAG, Log.DEBUG)) {
                            Log.d(TAG, "Successfully requested location updates");
                        }
                    } else {
                        Log.e(TAG,
                                "Failed in requesting location updates, "
                                        + "status code: "
                                        + status.getStatusCode()
                                        + ", message: "
                                        + status.getStatusMessage());
                    }
                }
            });
}

&#64;Override
protected void onPause() {
    super.onPause();
    if (mGoogleApiClient.isConnected()) {
        LocationServices.FusedLocationApi
             .removeLocationUpdates(mGoogleApiClient, this);
    }
    mGoogleApiClient.disconnect();
}

&#64;Override
public void onConnectionSuspended(int i) {
    if (Log.isLoggable(TAG, Log.DEBUG)) {
        Log.d(TAG, "connection to location client suspended");
    }
}

</pre>

<p>Now that you have enabled location updates, the system calls the {@link android.location.LocationListener#onLocationChanged
onLocationChanged()} method with the updated location at the interval specified in <a
href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setInterval(long)">
{@code setInterval()}</a>
</p>

<h2 id="DetectGPS">Detect On-Board GPS</h2>

<p>Not all wearables have a GPS sensor. If your user goes out for a run and leaves their phone at
home, your wearable app cannot receive location data through a tethered connection. If the
wearable device does not have a sensor, you should detect this situation and warn the user that
location functionality is not available.

<p>To determine whether your Android Wear device has a built-in GPS sensor, use the
{@link android.content.pm.PackageManager#hasSystemFeature hasSystemFeature()}
method. The following code detects whether the device has built-in GPS when you start an activity:
</p>

<pre>

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main_activity);
    if (!hasGps()) {
        Log.d(TAG, "This hardware doesn't have GPS.");
        // Fall back to functionality that does not use location or
        // warn the user that location function is not available.
    }

    ...
}

private boolean hasGps() {
    return getPackageManager().hasSystemFeature(PackageManager.FEATURE_LOCATION_GPS);
}
</pre>

<h2 id="Disconnection">Handle Disconnection Events</h2>

<p>Wearable devices relying on a tethered connection for location data may lose their connections
abruptly. If your wearable app expects a constant stream of data, you must handle the
disconnection based upon where that data is interrupted or unavailable. On a wearable device with no
onboard GPS sensor, loss of location data occurs when the device loses its tethered data connection.
</p>

<p>In cases where your app depends on a tethered data connection for location data and the wear
device does not have a GPS sensor, you should detect the loss of that connection, warn the user, and
gracefully degrade the functionality of your app.</p>

<p>To detect the loss of a tethered data connection:</p>

<ol>
  <li>Extend a <a href="{@docRoot}reference/com/google/android/gms/wearable/WearableListenerService.html">
  <code>WearableListenerService</code></a> that lets you listen for important data layer events.
  </li>
  <li>Declare an intent filter in your Android manifest to notify the system about your
  <a href="{@docRoot}reference/com/google/android/gms/wearable/WearableListenerService.html"><code>
  WearableListenerService</code></a>.
  This filter allows the system to bind your service as needed.
<pre>
&lt;service android:name=".NodeListenerService"&gt;
    &lt;intent-filter&gt;
        &lt;action android:name="com.google.android.gms.wearable.BIND_LISTENER" /&gt;
    &lt;/intent-filter&gt;
&lt;/service>
</pre>
  </li>
  <li>Implement the <a href="{@docRoot}reference/com/google/android/gms/wearable/WearableListenerService.html#onPeerDisconnected(com.google.android.gms.wearable.Node)">
  <code>onPeerDisconnected()</code></a> method and handle cases of whether or not the device has
  built-in
  GPS.
<pre>
public class NodeListenerService extends WearableListenerService {

    private static final String TAG = "NodeListenerService";

    &#64;Override
    public void onPeerDisconnected(Node peer) {
        Log.d(TAG, "You have been disconnected.");
        if(!hasGPS()) {
            // Notify user to bring tethered handset
            // Fall back to functionality that does not use location
        }
    }
    ...
}
</pre>
  </li>
</ol>

For more information, read the <a href="{@docRoot}training/wearables/data-layer/events.html#Listen">
Listen for Data Layer Events</a> guide.

<h2 id="Notify">Handle Location Not Found</h2>

<p>When the GPS signal is lost, you can still retrieve the last known location using
<a href="{@docRoot}reference/com/google/android/gms/location/FusedLocationProviderApi.html#getLastLocation(com.google.android.gms.common.api.GoogleApiClient)">
<code>getLastLocation()</code></a>. This method can be helpful in situations where you are unable to
get a GPS fix, or when your wearable doesn't have built-in GPS and loses its connection with the
phone.</p>

<p>The following code uses <a href="{@docRoot}reference/com/google/android/gms/location/FusedLocationProviderApi.html#getLastLocation(com.google.android.gms.common.api.GoogleApiClient)">
<code>getLastLocation()</code></a> to retrieve the last known location if available:
</p>

<pre>
Location location = LocationServices.FusedLocationApi
                .getLastLocation(mGoogleApiClient);
</pre>

<h2 id="Synchronize">Synchronize Data</h2>

<p>If your wearable app records data using the built-in GPS, you may want to synchronize
the location data with the handset. With the {@link android.location.LocationListener}, you
implement the {@link android.location.LocationListener#onLocationChanged onLocationChanged()}
method to detect and record the location as it changes.

<p>The following code for wearable apps detects when the location changes and uses the data layer
API to store the data for later retrieval by your phone app:</p>

<pre>
&#64;Override
public void onLocationChanged(Location location) {
    ...
    addLocationEntry(location.getLatitude(), location.getLongitude());

}

private void addLocationEntry(double latitude, double longitude) {
    if (!mSaveGpsLocation || !mGoogleApiClient.isConnected()) {
        return;
    }

    mCalendar.setTimeInMillis(System.currentTimeMillis());

    // Set the path of the data map
    String path = Constants.PATH + "/" + mCalendar.getTimeInMillis();
    PutDataMapRequest putDataMapRequest = PutDataMapRequest.create(path);

    // Set the location values in the data map
    putDataMapRequest.getDataMap()
            .putDouble(Constants.KEY_LATITUDE, latitude);
    putDataMapRequest.getDataMap()
            .putDouble(Constants.KEY_LONGITUDE, longitude);
    putDataMapRequest.getDataMap()
            .putLong(Constants.KEY_TIME, mCalendar.getTimeInMillis());

    // Prepare the data map for the request
    PutDataRequest request = putDataMapRequest.asPutDataRequest();

    // Request the system to create the data item
    Wearable.DataApi.putDataItem(mGoogleApiClient, request)
            .setResultCallback(new ResultCallback<DataApi.DataItemResult>() {
                &#64;Override
                public void onResult(DataApi.DataItemResult dataItemResult) {
                    if (!dataItemResult.getStatus().isSuccess()) {
                        Log.e(TAG, "Failed to set the data, "
                                + "status: " + dataItemResult.getStatus()
                                .getStatusCode());
                    }
                }
            });
}
</pre>

<p>For more information on how to use the Data Layer API, see the <a href="{@docRoot}training/
wearables/data-layer/index.html">Sending and Syncing Data</a>
guide.</p>