LocationUpdates.zip
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
LocationClient.getLastLocation(),
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.
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.
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.
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}.
For example, to add the coarse location permission to your manifest, insert the following as a
child element of
the
<manifest>
element:
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
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
GooglePlayServicesUtil.isGooglePlayServicesAvailable(),
which returns one of the
integer result codes listed in the API reference documentation. If you encounter an error,
call
GooglePlayServicesUtil.getErrorDialog()
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()}
Note: 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}.
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:
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.
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
return mDialog;
}
}
...
/*
* Handle results returned to the FragmentActivity
* by Google Play services
*/
@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");
}
}
}
...
}
Snippets in the following sections call this method to verify that Google Play services is available.
Before you request location updates, you must first implement the interfaces that Location Services uses to communicate connection status to your app:
ConnectionCallbacks
OnConnectionFailedListener
The following snippet shows how to specify the interfaces and define the methods:
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
*/
@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.
*/
@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.
*/
@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());
}
}
...
}
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 Recognizing the User's Current Activity, which presents a similar pattern.
The callback method that Location Services invokes to send a location update to your app is
specified in the
LocationListener
interface, in the method
onLocationChanged().
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:
public class MainActivity extends FragmentActivity implements
GooglePlayServicesClient.ConnectionCallbacks,
GooglePlayServicesClient.OnConnectionFailedListener,
LocationListener {
...
// Define the callback method that receives location updates
@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();
}
...
}
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.
Location Services allows you to control the interval between updates and the location accuracy
you want, by setting the values in a
LocationRequest
object and then sending this object as part of your request to start updates.
First, set the following interval parameters:
LocationRequest.setInterval().
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.
LocationRequest.setFastestInterval().
This method sets the fastest 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
LocationRequest.setInterval().
If this rate is faster than your app can handle, you may encounter problems with UI flicker
or data overflow. To prevent this, call
LocationRequest.setFastestInterval()
to set an upper limit to the update rate.
Calling
LocationRequest.setFastestInterval()
also helps to save power. When you request a preferred update rate by calling
LocationRequest.setInterval(),
and a maximum rate by calling
LocationRequest.setFastestInterval(),
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
LocationRequest.setInterval().
Next, set the accuracy parameter. In a foreground app, you need constant location updates with
high accuracy, so use the setting
LocationRequest.PRIORITY_HIGH_ACCURACY.
The following snippet shows how to set the update interval and accuracy in {@link android.support.v4.app.FragmentActivity#onCreate onCreate()}:
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;
...
@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);
...
}
...
}
Note: 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.
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
requestLocationUpdates().
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
ConnectionCallbacks.onConnected()
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()}.
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()}:
public class MainActivity extends FragmentActivity implements
GooglePlayServicesClient.ConnectionCallbacks,
GooglePlayServicesClient.OnConnectionFailedListener,
LocationListener {
...
// Global variables
...
LocationClient mLocationClient;
boolean mUpdatesRequested;
...
@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;
...
}
...
@Override
protected void onPause() {
// Save the current setting for updates
mEditor.putBoolean("KEY_UPDATES_ON", mUpdatesRequested);
mEditor.commit();
super.onPause();
}
...
@Override
protected void onStart() {
...
mLocationClient.connect();
}
...
@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();
}
}
...
/*
* 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
*/
@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);
}
}
...
}
For more information about saving preferences, read Saving Key-Value Sets.
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
removeLocationUpdates(LocationListener).
For example:
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.
*/
@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();
}
...
}
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.
The next lesson, Displaying a Location Address, shows you how to use the current location to display the current street address.