docs/html/training/location/receive-location-updates.jd

page.title=Receiving Location Updates
trainingnavtop=true
@jd:body

<div id="tb-wrapper">
  <div id="tb">

  <h2>This lesson teaches you how to</h2>
  <ol>
    <li><a href="#get-last-location">Get the Last Known Location</a></li>
    <li><a href="#updates">Request Location Updates</a></li>
    <li><a href="#callback">Define the Location Update Callback</a></li>
    <li><a href="#stop-updates">Stop Location Updates</a></li>
    <li><a href="#save-state">Save the State of the Activity</a></li>
  </ol>

  <h2>You should also read</h2>
  <ul>
    <li>
      <a href="{@docRoot}google/play-services/setup.html">Setting up Google Play
    Services</a>
    </li>
    <li>
      <a href="retrieve-current.html">Getting the Last Known Location</a>
    </li>
   </ul>

  <h2>Try it out</h2>

    <ul>
      <li>
        <a href="https://github.com/googlesamples/android-play-location/tree/master/LocationUpdates" class="external-link">LocationUpdates</a>
      </li>
    </ul>
  </div>
</div>

<p>If your app can continuously track location, it can deliver more relevant
  information to the user. For example, if your app helps the user find their
  way while walking or driving, or if your app tracks the location of assets, it
  needs to get the location of the device at regular intervals. As well as the
  geographical location (latitude and longitude), you may want to give the user
  further information such as the bearing (horizontal direction of travel),
  altitude, or velocity of the device. This information, and more, is available
  in the {@link android.location.Location} object that your app can retrieve
  from the
  <a href="{@docRoot}reference/com/google/android/gms/location/FusedLocationProviderApi.html">fused
  location provider</a>.</p>

<p>While you can get a device's location with
  <a href="{@docRoot}reference/com/google/android/gms/location/FusedLocationProviderApi.html#getLastLocation(com.google.android.gms.common.api.GoogleApiClient)">{@code getLastLocation()}</a>,
  as illustrated in the lesson on
  <a href="retrieve-current.html">Getting the Last Known Location</a>,
  a more direct approach is to request periodic updates from the fused location
  provider. In response, the API updates your app periodically with the best
  available location, based on the currently-available location providers such
  as WiFi and GPS (Global Positioning System). The accuracy of the location is
  determined by the providers, the location permissions you've requested, and
  the options you set in the location request.</p>

<p>This lesson shows you how to request regular updates about a device's
  location using the
  <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()}</a>
  method in the fused location provider.

<h2 id="get-last-location">Get the Last Known Location</h2>

<p>The last known location of the device provides a handy base from which to
  start, ensuring that the app has a known location before starting the
  periodic location updates. The lesson on
  <a href="retrieve-current.html">Getting the Last Known Location</a> shows you
  how to get the last known location by calling
  <a href="{@docRoot}reference/com/google/android/gms/location/FusedLocationProviderApi.html#getLastLocation(com.google.android.gms.common.api.GoogleApiClient)">{@code getLastLocation()}</a>.
  The snippets in the following sections assume that your app has already
  retrieved the last known location and stored it as a
  {@link android.location.Location} object in the global variable
  {@code mCurrentLocation}.</p>

<p>Apps that use location services must request location permissions. In this
  lesson you require fine location detection, so that your app can get as
  precise a location as possible from the available location providers. Request
  this permission with the
  {@code uses-permission} element in your app manifest, as shown in the
  following example:</p>

<pre>
&lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.google.android.gms.location.sample.locationupdates" &gt;

  &lt;uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/&gt;
&lt;/manifest&gt;
</pre>

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

<p>Before requesting location updates, your app must connect to location
  services and make a location request. The lesson on
  <a href="change-location-settings.html">Changing Location Settings</a>
  shows you how to do this. Once a location request is in place you can start
  the regular updates by calling
  <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()}</a>.
  Do this in the
  <a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.ConnectionCallbacks.html#onConnected(android.os.Bundle)">{@code onConnected()}</a>
  callback provided by Google API Client, which is called when the client is
  ready.</p>

<p>Depending on the form of the request, the fused location provider either
  invokes the
  <a href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html">{@code LocationListener.onLocationChanged()}</a>
  callback method and passes it a {@link android.location.Location} object, or
  issues a
  <a href="{@docRoot}reference/android/app/PendingIntent.html">{@code PendingIntent}</a>
  that contains the location in its extended data. The accuracy and frequency of
  the updates are affected by the location permissions you've requested and the
  options you set in the location request object.</p>

<p>This lesson shows you how to get the update using the
  <a href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html">{@code LocationListener}</a>
  callback approach. Call
  <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()}</a>,
  passing it your instance of the
  <a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.html">{@code GoogleApiClient}</a>,
  the
  <a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html">{@code LocationRequest}</a>
  object,
  and a <a href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html">{@code LocationListener}</a>.
  Define a {@code startLocationUpdates()} method, called from the
  <a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.ConnectionCallbacks.html#onConnected(android.os.Bundle)">{@code onConnected()}</a>
  callback, as shown in the following code sample:</p>

<pre>
&#64;Override
public void onConnected(Bundle connectionHint) {
    ...
    if (mRequestingLocationUpdates) {
        startLocationUpdates();
    }
}

protected void startLocationUpdates() {
    LocationServices.FusedLocationApi.requestLocationUpdates(
            mGoogleApiClient, mLocationRequest, this);
}
</pre>

<p>Notice that the above code snippet refers to a boolean flag,
  {@code mRequestingLocationUpdates}, used to track whether the user has
  turned location updates on or off. For more about retaining the value of this
  flag across instances of the activity, see
  <a href="#save-state">Save the State of the Activity</a>.

<h2 id="callback">Define the Location Update Callback</h2>

<p>The fused location provider invokes the
  <a href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html#onLocationChanged(android.location.Location)">{@code LocationListener.onLocationChanged()}</a>
  callback method. The incoming argument is a {@link android.location.Location}
  object containing the location's latitude and longitude. The following snippet
  shows how to implement the
  <a href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html">{@code LocationListener}</a>
  interface and define the method, then get the timestamp of the location update
  and display the latitude, longitude and timestamp on your app's user
  interface:</p>

<pre>
public class MainActivity extends ActionBarActivity implements
        ConnectionCallbacks, OnConnectionFailedListener, LocationListener {
    ...
    &#64;Override
    public void onLocationChanged(Location location) {
        mCurrentLocation = location;
        mLastUpdateTime = DateFormat.getTimeInstance().format(new Date());
        updateUI();
    }

    private void updateUI() {
        mLatitudeTextView.setText(String.valueOf(mCurrentLocation.getLatitude()));
        mLongitudeTextView.setText(String.valueOf(mCurrentLocation.getLongitude()));
        mLastUpdateTimeTextView.setText(mLastUpdateTime);
    }
}
</pre>

<h2 id="stop-updates">Stop Location Updates</h2>

<p>Consider whether you want to stop the location updates when the activity is
  no longer in focus, such as when the user switches to another app or to a
  different activity in the same app. This can be handy to reduce power
  consumption, provided the app doesn't need to collect information even when
  it's running in the background. This section shows how you can stop the
  updates in the activity's
  {@link android.app.Activity#onPause onPause()} method.</p>

<p>To stop location updates, call
  <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()}</a>,
  passing it your instance of the
  <a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.html">{@code GoogleApiClient}</a>
  object and a
  <a href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html">{@code LocationListener}</a>,
  as shown in the following code sample:</p>

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

protected void stopLocationUpdates() {
    LocationServices.FusedLocationApi.removeLocationUpdates(
            mGoogleApiClient, this);
}
</pre>

<p>Use a boolean, {@code mRequestingLocationUpdates}, to track
  whether location updates are currently turned on. In the activity's
  {@link android.app.Activity#onResume onResume()} method, check
  whether location updates are currently active, and activate them if not:</p>

<pre>
&#64;Override
public void onResume() {
    super.onResume();
    if (mGoogleApiClient.isConnected() && !mRequestingLocationUpdates) {
        startLocationUpdates();
    }
}
</pre>

<h2 id="save-state">Save the State of the Activity</h2>

<p>A change to the device's configuration, such as a change in screen
  orientation or language, can cause the current activity to be destroyed. Your
  app must therefore store any information it needs to recreate the activity.
  One way to do this is via an instance state stored in a
  {@link android.os.Bundle} object.</p>

<p>The following code sample shows how to use the activity's
  <a href="{@docRoot}reference/android/app/Activity.html#onSaveInstanceState(android.os.Bundle)">{@code onSaveInstanceState()}</a>
  callback to save the instance state:</p>

<pre>
public void onSaveInstanceState(Bundle savedInstanceState) {
    savedInstanceState.putBoolean(REQUESTING_LOCATION_UPDATES_KEY,
            mRequestingLocationUpdates);
    savedInstanceState.putParcelable(LOCATION_KEY, mCurrentLocation);
    savedInstanceState.putString(LAST_UPDATED_TIME_STRING_KEY, mLastUpdateTime);
    super.onSaveInstanceState(savedInstanceState);
}
</pre>

<p>Define an {@code updateValuesFromBundle()} method to restore
  the saved values from the previous instance of the activity, if they're
  available. Call the method from the activity's
  {@link android.app.Activity#onCreate onCreate()} method, as shown in the
  following code sample:</p>

<pre>
&#64;Override
public void onCreate(Bundle savedInstanceState) {
    ...
    updateValuesFromBundle(savedInstanceState);
}

private void updateValuesFromBundle(Bundle savedInstanceState) {
    if (savedInstanceState != null) {
        // Update the value of mRequestingLocationUpdates from the Bundle, and
        // make sure that the Start Updates and Stop Updates buttons are
        // correctly enabled or disabled.
        if (savedInstanceState.keySet().contains(REQUESTING_LOCATION_UPDATES_KEY)) {
            mRequestingLocationUpdates = savedInstanceState.getBoolean(
                    REQUESTING_LOCATION_UPDATES_KEY);
            setButtonsEnabledState();
        }

        // Update the value of mCurrentLocation from the Bundle and update the
        // UI to show the correct latitude and longitude.
        if (savedInstanceState.keySet().contains(LOCATION_KEY)) {
            // Since LOCATION_KEY was found in the Bundle, we can be sure that
            // mCurrentLocationis not null.
            mCurrentLocation = savedInstanceState.getParcelable(LOCATION_KEY);
        }

        // Update the value of mLastUpdateTime from the Bundle and update the UI.
        if (savedInstanceState.keySet().contains(LAST_UPDATED_TIME_STRING_KEY)) {
            mLastUpdateTime = savedInstanceState.getString(
                    LAST_UPDATED_TIME_STRING_KEY);
        }
        updateUI();
    }
}
</pre>

<p>For more about saving instance state, see the
  <a href="{@docRoot}reference/android/app/Activity.html#ConfigurationChanges">Android
  Activity</a> class reference.</p>

<p class="note"><strong>Note:</strong> For a more persistent storage, you can
  store the user's preferences in your app's
  {@link android.content.SharedPreferences}. Set the shared preference in
  your activity's {@link android.app.Activity#onPause onPause()} method, and
  retrieve the preference in {@link android.app.Activity#onResume onResume()}.
  For more information about saving preferences, read
  <a href="{@docRoot}training/basics/data-storage/shared-preferences.html">Saving
  Key-Value Sets</a>.</p>

<p>The next lesson,
  <a href="display-address.html">Displaying a Location Address</a>, shows
  you how to display the street address for a given location.</p>