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Merge "docs: Updates the request-location-updates lesson in the location APIs training course." into lmp-docs

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Sarah Maddox
2014-12-18 19:42:34 +00:00
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page.title=Receiving Location Updates
trainingnavtop=true
@jd:body
<div id="tb-wrapper">
<div id="tb">
<div id="tb">
<h2>This lesson teaches you to</h2>
<ol>
<li><a href="#Permissions">Request Location Permission</a></li>
<li><a href="#PlayServices">Check for Google Play Services</a></li>
<li><a href="#DefineCallbacks">Define Location Services Callbacks</a></li>
<li><a href="#UpdateParameters">Specify Update Parameters</a></li>
<li><a href="#StartUpdates">Start Location Updates</a></li>
<li><a href="#StopUpdates">Stop Location Updates</a></li>
</ol>
<h2>This lesson teaches you how to</h2>
<ol>
<li><a href="#connect">Connect to Location Services</a></li>
<li><a href="#location-request">Set Up a Location Request</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>
<h2>You should also read</h2>
<ul>
<li>
<a href="{@docRoot}google/play-services/setup.html">Setup Google Play Services SDK</a>
<a href="{@docRoot}google/play-services/setup.html">Setting up Google Play
Services</a>
</li>
<li>
<a href="retrieve-current.html">Retrieving the Current Location</a>
<a href="retrieve-current.html">Getting the Last Known Location</a>
</li>
</ul>
</ul>
<h2>Try it out</h2>
<h2>Try it out</h2>
<div class="download-box">
<a href="http://developer.android.com/shareables/training/LocationUpdates.zip" class="button">Download the sample</a>
<p class="filename">LocationUpdates.zip</p>
<ul>
<li>
<a href="https://github.com/googlesamples/android-play-location/tree/master/LocationUpdates" class="external-link">LocationUpdates</a>
</li>
</ul>
</div>
</div>
</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="connect">Connect to Location Services</h2>
<p>Location services for apps are provided through Google Play services and the
fused location provider. In order to use these services, you connect your app
using the Google API Client and then request location updates. For details on
connecting with the
<a href="{@docRoot}reference/com/google/android/gms/common/api/GoogleApiClient.html">{@code GoogleApiClient}</a>,
follow the instructions in
<a href="retrieve-current.html">Getting the Last Known Location</a>, including
requesting the current location.</p>
<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>
<p>
If your app does navigation or tracking, you probably want to get the user's
location at regular intervals. While you can do this with
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationClient.html#getLastLocation()">LocationClient.getLastLocation()</a></code>,
a more direct approach is to request periodic updates from Location Services. In
response, Location Services automatically updates your app with the best available location,
based on the currently-available location providers such as WiFi and GPS.
</p>
<p>
To get periodic location updates from Location Services, you send a request using a location
client. Depending on the form of the request, Location Services either invokes a callback
method and passes in a {@link android.location.Location} object, or issues an
{@link android.content.Intent} 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
parameters you pass to Location Services with the request.
</p>
<!-- Request permission -->
<h2 id="Permissions">Specify App Permissions</h2>
<p>
Apps that use Location Services must request location permissions. Android has two location
permissions, {@link android.Manifest.permission#ACCESS_COARSE_LOCATION ACCESS_COARSE_LOCATION}
and {@link android.Manifest.permission#ACCESS_FINE_LOCATION ACCESS_FINE_LOCATION}. The
permission you choose affects the accuracy of the location updates you receive.
For example, If you request only coarse location permission, Location Services obfuscates the
updated location to an accuracy that's roughly equivalent to a city block.
</p>
<p>
Requesting {@link android.Manifest.permission#ACCESS_FINE_LOCATION ACCESS_FINE_LOCATION} implies
a request for {@link android.Manifest.permission#ACCESS_COARSE_LOCATION ACCESS_COARSE_LOCATION}.
</p>
<p>
For example, to add the coarse location permission to your manifest, insert the following as a
child element of
the
<code><a href="{@docRoot}guide/topics/manifest/manifest-element.html">&lt;manifest&gt;</a></code>
element:
</p>
<pre>
&lt;uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/&gt;
</pre>
<!-- Check for Google Play services -->
<h2 id="PlayServices">Check for Google Play Services</h2>
<p>
Location Services is part of the Google Play services APK. Since it's hard to anticipate the
state of the user's device, you should always check that the APK is installed before you attempt
to connect to Location Services. To check that the APK is installed, call
<code><a href="{@docRoot}reference/com/google/android/gms/common/GooglePlayServicesUtil.html#isGooglePlayServicesAvailable(android.content.Context)">GooglePlayServicesUtil.isGooglePlayServicesAvailable()</a></code>,
which returns one of the
integer result codes listed in the API reference documentation. If you encounter an error,
call
<code><a href="{@docRoot}reference/com/google/android/gms/common/GooglePlayServicesUtil.html#getErrorDialog(int, android.app.Activity, int)">GooglePlayServicesUtil.getErrorDialog()</a></code>
to retrieve localized dialog that prompts users to take the correct action, then display
the dialog in a {@link android.support.v4.app.DialogFragment}. The dialog may allow the
user to correct the problem, in which case Google Play services may send a result back to your
activity. To handle this result, override the method
{@link android.support.v4.app.FragmentActivity#onActivityResult onActivityResult()}
&lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.google.android.gms.location.sample.locationupdates" &gt;
</p>
<p class="note">
<strong>Note:</strong> To make your app compatible with
platform version 1.6 and later, the activity that displays the
{@link android.support.v4.app.DialogFragment} must subclass
{@link android.support.v4.app.FragmentActivity} instead of {@link android.app.Activity}. Using
{@link android.support.v4.app.FragmentActivity} also allows you to call
{@link android.support.v4.app.FragmentActivity#getSupportFragmentManager
getSupportFragmentManager()} to display the {@link android.support.v4.app.DialogFragment}.
</p>
<p>
Since you usually need to check for Google Play services in more than one place in your code,
define a method that encapsulates the check, then call the method before each connection
attempt. The following snippet contains all of the code required to check for Google
Play services:
</p>
<pre>
public class MainActivity extends FragmentActivity {
...
// Global constants
/*
* Define a request code to send to Google Play services
* This code is returned in Activity.onActivityResult
*/
private final static int
CONNECTION_FAILURE_RESOLUTION_REQUEST = 9000;
...
// Define a DialogFragment that displays the error dialog
public static class ErrorDialogFragment extends DialogFragment {
// Global field to contain the error dialog
private Dialog mDialog;
// Default constructor. Sets the dialog field to null
public ErrorDialogFragment() {
super();
mDialog = null;
}
// Set the dialog to display
public void setDialog(Dialog dialog) {
mDialog = dialog;
}
// Return a Dialog to the DialogFragment.
&#64;Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
return mDialog;
}
}
...
/*
* Handle results returned to the FragmentActivity
* by Google Play services
*/
&#64;Override
protected void onActivityResult(
int requestCode, int resultCode, Intent data) {
// Decide what to do based on the original request code
switch (requestCode) {
...
case CONNECTION_FAILURE_RESOLUTION_REQUEST :
/*
* If the result code is Activity.RESULT_OK, try
* to connect again
*/
switch (resultCode) {
case Activity.RESULT_OK :
/*
* Try the request again
*/
...
break;
}
...
}
...
}
...
private boolean servicesConnected() {
// Check that Google Play services is available
int resultCode =
GooglePlayServicesUtil.
isGooglePlayServicesAvailable(this);
// If Google Play services is available
if (ConnectionResult.SUCCESS == resultCode) {
// In debug mode, log the status
Log.d("Location Updates",
"Google Play services is available.");
// Continue
return true;
// Google Play services was not available for some reason
} else {
// Get the error code
int errorCode = connectionResult.getErrorCode();
// Get the error dialog from Google Play services
Dialog errorDialog = GooglePlayServicesUtil.getErrorDialog(
errorCode,
this,
CONNECTION_FAILURE_RESOLUTION_REQUEST);
// If Google Play services can provide an error dialog
if (errorDialog != null) {
// Create a new DialogFragment for the error dialog
ErrorDialogFragment errorFragment =
new ErrorDialogFragment();
// Set the dialog in the DialogFragment
errorFragment.setDialog(errorDialog);
// Show the error dialog in the DialogFragment
errorFragment.show(
getSupportFragmentManager(),
"Location Updates");
}
}
}
...
}
&lt;uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/&gt;
&lt;/manifest&gt;
</pre>
<p>
Snippets in the following sections call this method to verify that Google Play services is
available.
</p>
<!--
Define Location Services Callbacks
-->
<h2 id="DefineCallbacks">Define Location Services Callbacks</h2>
<p>
Before you request location updates, you must first implement the interfaces that Location
Services uses to communicate connection status to your app:
</p>
<h2 id="location-request">Set Up a Location Request</h2>
<p>To store parameters for requests to the fused location provider, create a
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html">{@code LocationRequest}</a>.
The parameters determine the levels of accuracy requested. For details of all
the options available in the location request, see the
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html">{@code LocationRequest}</a>
class reference. This lesson sets the update interval, fastest update
interval, and priority, as described below:</p>
<dl>
<dt>
<code><a href="{@docRoot}reference/com/google/android/gms/common/GooglePlayServicesClient.ConnectionCallbacks.html">ConnectionCallbacks</a></code>
</dt>
<dd>
Specifies methods that Location Services calls when a location client is connected or
disconnected.
</dd>
<dt>
<code><a href="{@docRoot}reference/com/google/android/gms/common/GooglePlayServicesClient.OnConnectionFailedListener.html">OnConnectionFailedListener</a></code>
</dt>
<dd>
Specifies a method that Location Services calls if an error occurs while attempting to
connect the location client. This method uses the previously-defined {@code showErrorDialog}
method to display an error dialog that attempts to fix the problem using Google Play
services.
</dd>
<dt>
Update interval
</dt>
<dd>
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setInterval(long)">{@code setInterval()}</a>
- This method sets the rate in milliseconds at which your app prefers to
receive location updates. Note that the location updates may be faster than
this rate if another app is receiving updates at a faster rate, or slower
than this rate, or there may be no updates at all (if the device has no
connectivity, for example).
</dd>
<dt>
Fastest update interval
</dt>
<dd>
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setFastestInterval(long)">{@code setFastestInterval()}</a>
- This method sets the <strong>fastest</strong> rate in milliseconds at which
your app can handle location updates. You need to set this rate because
other apps also affect the rate at which updates are sent. The Google Play
services location APIs send out updates at the fastest rate that any app
has requested with
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setInterval(long)">{@code setInterval()}</a>.
If this rate is faster
than your app can handle, you may encounter problems with UI flicker or data
overflow. To prevent this, call
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setFastestInterval(long)">{@code setFastestInterval()}</a>
to set an upper limit to the update rate.
</dd>
<dt>Priority</dt>
<dd>
<p>
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setPriority(int)">{@code setPriority()}</a>
- This method sets the priority of the request, which gives the Google Play
services location services a strong hint about which location sources to use.
The following values are supported:</p>
<ul>
<li>
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#PRIORITY_BALANCED_POWER_ACCURACY">{@code PRIORITY_BALANCED_POWER_ACCURACY}</a>
- Use this setting to request location precision to within a city
block, which is an accuracy of approximately 100 meters. This is
considered a coarse level of accuracy, and is likely to consume less
power. With this setting, the location services are likely to use WiFi
and cell tower positioning. Note, however, that the choice of location
provider depends on many other factors, such as which sources are
available.</li>
<li>
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#PRIORITY_HIGH_ACCURACY">{@code PRIORITY_HIGH_ACCURACY}</a>
- Use this setting to request the most precise location possible. With
this setting, the location services are more likely to use GPS
(Global Positioning System) to determine the location.</li>
<li><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#PRIORITY_LOW_POWER">{@code PRIORITY_LOW_POWER}</a>
- Use this setting to request city-level precision, which is
an accuracy of approximately 10 kilometers. This is considered a
coarse level of accuracy, and is likely to consume less power.</li>
<li><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#PRIORITY_NO_POWER">{@code PRIORITY_NO_POWER}</a>
- Use this setting if you need negligible impact on power consumption,
but want to receive location updates when available. With this
setting, your app does not trigger any location updates, but
receives locations triggered by other apps.</li>
</ul>
</dd>
</dl>
<p>
The following snippet shows how to specify the interfaces and define the methods:
</p>
<p>Create the location request and set the parameters as shown in this
code sample:</p>
<pre>
public class MainActivity extends FragmentActivity implements
GooglePlayServicesClient.ConnectionCallbacks,
GooglePlayServicesClient.OnConnectionFailedListener {
...
/*
* Called by Location Services when the request to connect the
* client finishes successfully. At this point, you can
* request the current location or start periodic updates
*/
&#64;Override
public void onConnected(Bundle dataBundle) {
// Display the connection status
Toast.makeText(this, "Connected", Toast.LENGTH_SHORT).show();
}
...
/*
* Called by Location Services if the connection to the
* location client drops because of an error.
*/
&#64;Override
public void onDisconnected() {
// Display the connection status
Toast.makeText(this, "Disconnected. Please re-connect.",
Toast.LENGTH_SHORT).show();
}
...
/*
* Called by Location Services if the attempt to
* Location Services fails.
*/
&#64;Override
public void onConnectionFailed(ConnectionResult connectionResult) {
/*
* Google Play services can resolve some errors it detects.
* If the error has a resolution, try sending an Intent to
* start a Google Play services activity that can resolve
* error.
*/
if (connectionResult.hasResolution()) {
try {
// Start an Activity that tries to resolve the error
connectionResult.startResolutionForResult(
this,
CONNECTION_FAILURE_RESOLUTION_REQUEST);
/*
* Thrown if Google Play services canceled the original
* PendingIntent
*/
} catch (IntentSender.SendIntentException e) {
// Log the error
e.printStackTrace();
}
} else {
/*
* If no resolution is available, display a dialog to the
* user with the error.
*/
showErrorDialog(connectionResult.getErrorCode());
}
}
...
protected void createLocationRequest() {
LocationRequest mLocationRequest = new LocationRequest();
mLocationRequest.setInterval(10000);
mLocationRequest.setFastestInterval(5000);
mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
}
</pre>
<h3>Define the location update callback</h3>
<p>
Location Services sends location updates to your app either as an {@link android.content.Intent}
or as an argument passed to a callback method you define. This lesson shows you how to get the
update using a callback method, because that pattern works best for most use cases. If you want
to receive updates in the form of an {@link android.content.Intent}, read the lesson
<a href="activity-recognition.html">Recognizing the User's Current Activity</a>, which
presents a similar pattern.
</p>
<p>
The callback method that Location Services invokes to send a location update to your app is
specified in the
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html">LocationListener</a></code>
interface, in the method
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationListener.html#onLocationChanged(android.location.Location)">onLocationChanged()</a></code>.
The incoming argument is a {@link android.location.Location} object containing the location's
latitude and longitude. The following snippet shows how to specify the interface and define
the method:
</p>
<p>The priority of
<a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#PRIORITY_HIGH_ACCURACY">{@code PRIORITY_HIGH_ACCURACY}</a>,
combined with the
{@link android.Manifest.permission#ACCESS_FINE_LOCATION ACCESS_FINE_LOCATION}
permission setting that you've defined in the app manifest, and a fast update
interval of 5000 milliseconds (5 seconds), causes the fused location
provider to return location updates that are accurate to within a few feet.
This approach is appropriate for mapping apps that display the location in
real time.</p>
<p class="note"><strong>Performance hint:</strong> If your app accesses the
network or does other long-running work after receiving a location update,
adjust the fastest interval to a slower value. This adjustment prevents your
app from receiving updates it can't use. Once the long-running work is done,
set the fastest interval back to a fast value.</p>
<h2 id="updates">Request Location Updates</h2>
<p>Now that you've set up a location request containing your app's requirements
for the location updates, 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>
public class MainActivity extends FragmentActivity implements
GooglePlayServicesClient.ConnectionCallbacks,
GooglePlayServicesClient.OnConnectionFailedListener,
LocationListener {
&#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 {
...
// Define the callback method that receives location updates
&#64;Override
public void onLocationChanged(Location location) {
// Report to the UI that the location was updated
String msg = "Updated Location: " +
Double.toString(location.getLatitude()) + "," +
Double.toString(location.getLongitude());
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
mCurrentLocation = location;
mLastUpdateTime = DateFormat.getTimeInstance().format(new Date());
updateUI();
}
...
}
</pre>
<p>
Now that you have the callbacks prepared, you can set up the request for location updates.
The first step is to specify the parameters that control the updates.
</p>
<!-- Specify update parameters -->
<h2 id="UpdateParameters">Specify Update Parameters</h2>
<p>
Location Services allows you to control the interval between updates and the location accuracy
you want, by setting the values in a
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html">LocationRequest</a></code>
object and then sending this object as part of your request to start updates.
</p>
<p>
First, set the following interval parameters:
</p>
<dl>
<dt>
Update interval
</dt>
<dd>
Set by
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setInterval(long)">LocationRequest.setInterval()</a></code>.
This method sets the rate in milliseconds at which your app prefers to receive location
updates. If no other apps are receiving updates from Location Services, your app will
receive updates at this rate.
</dd>
<dt>
Fastest update interval
</dt>
<dd>
Set by
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setFastestInterval(long)">LocationRequest.setFastestInterval()</a></code>.
This method sets the <b>fastest</b> rate in milliseconds at which your app can handle
location updates. You need to set this rate because other apps also affect the rate
at which updates are sent. Location Services sends out updates at the fastest rate that any
app requested by calling
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setInterval(long)">LocationRequest.setInterval()</a></code>.
If this rate is faster than your app can handle, you may encounter problems with UI flicker
or data overflow. To prevent this, call
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setFastestInterval(long)">LocationRequest.setFastestInterval()</a></code>
to set an upper limit to the update rate.
<p>
Calling
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setFastestInterval(long)">LocationRequest.setFastestInterval()</a></code>
also helps to save power. When you request a preferred update rate by calling
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setInterval(long)">LocationRequest.setInterval()</a></code>,
and a maximum rate by calling
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setFastestInterval(long)">LocationRequest.setFastestInterval()</a></code>,
then your app gets the same update rate as the fastest rate in the system. If other
apps have requested a faster rate, you get the benefit of a faster rate. If no other
apps have a faster rate request outstanding, your app receives updates at the rate you specified
with
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#setInterval(long)">LocationRequest.setInterval()</a></code>.
</p>
</dd>
</dl>
<p>
Next, set the accuracy parameter. In a foreground app, you need constant location updates with
high accuracy, so use the setting
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationRequest.html#PRIORITY_HIGH_ACCURACY">LocationRequest.PRIORITY_HIGH_ACCURACY</a></code>.
</p>
<p>
The following snippet shows how to set the update interval and accuracy in
{@link android.support.v4.app.FragmentActivity#onCreate onCreate()}:
</p>
<pre>
public class MainActivity extends FragmentActivity implements
GooglePlayServicesClient.ConnectionCallbacks,
GooglePlayServicesClient.OnConnectionFailedListener,
LocationListener {
...
// Global constants
...
// Milliseconds per second
private static final int MILLISECONDS_PER_SECOND = 1000;
// Update frequency in seconds
public static final int UPDATE_INTERVAL_IN_SECONDS = 5;
// Update frequency in milliseconds
private static final long UPDATE_INTERVAL =
MILLISECONDS_PER_SECOND * UPDATE_INTERVAL_IN_SECONDS;
// The fastest update frequency, in seconds
private static final int FASTEST_INTERVAL_IN_SECONDS = 1;
// A fast frequency ceiling in milliseconds
private static final long FASTEST_INTERVAL =
MILLISECONDS_PER_SECOND * FASTEST_INTERVAL_IN_SECONDS;
...
// Define an object that holds accuracy and frequency parameters
LocationRequest mLocationRequest;
...
&#64;Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Create the LocationRequest object
mLocationRequest = LocationRequest.create();
// Use high accuracy
mLocationRequest.setPriority(
LocationRequest.PRIORITY_HIGH_ACCURACY);
// Set the update interval to 5 seconds
mLocationRequest.setInterval(UPDATE_INTERVAL);
// Set the fastest update interval to 1 second
mLocationRequest.setFastestInterval(FASTEST_INTERVAL);
...
}
...
}
</pre>
<p class="note">
<strong>Note:</strong> If your app accesses the network or does other long-running work after
receiving a location update, adjust the fastest interval to a slower value. This prevents your
app from receiving updates it can't use. Once the long-running work is done, set the fastest
interval back to a fast value.
</p>
<!-- Start Location Updates -->
<h2 id="StartUpdates">Start Location Updates</h2>
<p>
To send the request for location updates, create a location client in
{@link android.support.v4.app.FragmentActivity#onCreate onCreate()}, then connect it and make
the request by calling
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationClient.html#requestLocationUpdates(com.google.android.gms.location.LocationRequest, com.google.android.gms.location.LocationListener)">requestLocationUpdates()</a></code>.
Since your client must be connected for your app to receive updates, you should
connect the client in
{@link android.support.v4.app.FragmentActivity#onStart onStart()}. This ensures that you always
have a valid, connected client while your app is visible. Since you need a connection before you
can request updates, make the update request in
<code><a href="{@docRoot}reference/com/google/android/gms/common/GooglePlayServicesClient.ConnectionCallbacks.html#onConnected(android.os.Bundle)">ConnectionCallbacks.onConnected()</a></code>
</p>
<p>
Remember that the user may want to turn off location updates for various reasons. You should
provide a way for the user to do this, and you should ensure that you don't start updates in
{@link android.support.v4.app.FragmentActivity#onStart onStart()} if updates were previously
turned off. To track the user's preference, store it in your app's
{@link android.content.SharedPreferences} in
{@link android.support.v4.app.FragmentActivity#onPause onPause()} and retrieve it in
{@link android.support.v4.app.FragmentActivity#onResume onResume()}.
</p>
<p>
The following snippet shows how to set up the client in
{@link android.support.v4.app.FragmentActivity#onCreate onCreate()}, and how to connect it
and request updates in {@link android.support.v4.app.FragmentActivity#onStart onStart()}:
</p>
<pre>
public class MainActivity extends FragmentActivity implements
GooglePlayServicesClient.ConnectionCallbacks,
GooglePlayServicesClient.OnConnectionFailedListener,
LocationListener {
...
// Global variables
...
LocationClient mLocationClient;
boolean mUpdatesRequested;
...
&#64;Override
protected void onCreate(Bundle savedInstanceState) {
...
// Open the shared preferences
mPrefs = getSharedPreferences("SharedPreferences",
Context.MODE_PRIVATE);
// Get a SharedPreferences editor
mEditor = mPrefs.edit();
/*
* Create a new location client, using the enclosing class to
* handle callbacks.
*/
mLocationClient = new LocationClient(this, this, this);
// Start with updates turned off
mUpdatesRequested = false;
...
}
...
&#64;Override
protected void onPause() {
// Save the current setting for updates
mEditor.putBoolean("KEY_UPDATES_ON", mUpdatesRequested);
mEditor.commit();
super.onPause();
}
...
&#64;Override
protected void onStart() {
...
mLocationClient.connect();
}
...
&#64;Override
protected void onResume() {
/*
* Get any previous setting for location updates
* Gets "false" if an error occurs
*/
if (mPrefs.contains("KEY_UPDATES_ON")) {
mUpdatesRequested =
mPrefs.getBoolean("KEY_UPDATES_ON", false);
// Otherwise, turn off location updates
} else {
mEditor.putBoolean("KEY_UPDATES_ON", false);
mEditor.commit();
}
private void updateUI() {
mLatitudeTextView.setText(String.valueOf(mCurrentLocation.getLatitude()));
mLongitudeTextView.setText(String.valueOf(mCurrentLocation.getLongitude()));
mLastUpdateTimeTextView.setText(mLastUpdateTime);
}
...
/*
* Called by Location Services when the request to connect the
* client finishes successfully. At this point, you can
* request the current location or start periodic updates
*/
&#64;Override
public void onConnected(Bundle dataBundle) {
// Display the connection status
Toast.makeText(this, "Connected", Toast.LENGTH_SHORT).show();
// If already requested, start periodic updates
if (mUpdatesRequested) {
mLocationClient.requestLocationUpdates(mLocationRequest, this);
}
}
...
}
</pre>
<p>
For more information about saving preferences, read
<a href="{@docRoot}training/basics/data-storage/shared-preferences.html">Saving Key-Value Sets</a>.
</p>
<!--
Stop Location Updates
-->
<h2 id="StopUpdates">Stop Location Updates</h2>
<p>
To stop location updates, save the state of the update flag in
{@link android.support.v4.app.FragmentActivity#onPause onPause()}, and stop updates in
{@link android.support.v4.app.FragmentActivity#onStop onStop()} by calling
<code><a href="{@docRoot}reference/com/google/android/gms/location/LocationClient.html#removeLocationUpdates(com.google.android.gms.location.LocationListener)">removeLocationUpdates(LocationListener)</a></code>.
For example:
</p>
<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>
public class MainActivity extends FragmentActivity implements
GooglePlayServicesClient.ConnectionCallbacks,
GooglePlayServicesClient.OnConnectionFailedListener,
LocationListener {
...
/*
* Called when the Activity is no longer visible at all.
* Stop updates and disconnect.
*/
&#64;Override
protected void onStop() {
// If the client is connected
if (mLocationClient.isConnected()) {
/*
* Remove location updates for a listener.
* The current Activity is the listener, so
* the argument is "this".
*/
removeLocationUpdates(this);
}
/*
* After disconnect() is called, the client is
* considered "dead".
*/
mLocationClient.disconnect();
super.onStop();
}
...
&#64;Override
protected void onPause() {
super.onPause();
stopLocationUpdates();
}
protected void stopLocationUpdates() {
LocationServices.FusedLocationApi.removeLocationUpdates(
mGoogleApiClient, this);
}
</pre>
<p>
You now have the basic structure of an app that requests and receives periodic location updates.
You can combine the features described in this lesson with the geofencing, activity recognition,
or reverse geocoding features described in other lessons in this class.
</p>
<p>
The next lesson, <a href="display-address.html">Displaying a Location Address</a>, shows you how
to use the current location to display the current street address.
</p>
<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>