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 Location
object that your app can retrieve
from the
fused
location provider.
While you can get a device's location with
getLastLocation()
,
as illustrated in the lesson on
Getting the Last Known Location,
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.
This lesson shows you how to request regular updates about a device's
location using the
requestLocationUpdates()
method in the fused location provider.
Get the last known location
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
Getting the Last Known Location shows you
how to get the last known location by calling
getLastLocation()
.
The snippets in the following sections assume that your app has already
retrieved the last known location and stored it as a
Location
object in the global variable
mCurrentLocation
.
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
uses-permission
element in your app manifest, as shown in the
following example:
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.google.android.gms.location.sample.locationupdates" > <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/> </manifest>
Request location updates
Before requesting location updates, your app must connect to location
services and make a location request. The lesson on
Changing Location Settings
shows you how to do this. Once a location request is in place you can start
the regular updates by calling
requestLocationUpdates()
.
Depending on the form of the request, the fused location provider either
invokes the
LocationCallback.onLocationResult()
callback method and passes it a list of Location
objects, or
issues a
PendingIntent
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.
This lesson shows you how to get the update using the
LocationCallback
callback approach. Call
requestLocationUpdates()
,
passing it your instance of the
LocationRequest
object,
and a LocationCallback
.
Define a startLocationUpdates()
method as shown in the following code sample:
Kotlin
override fun onResume() { super.onResume() if (requestingLocationUpdates) startLocationUpdates() } private fun startLocationUpdates() { fusedLocationClient.requestLocationUpdates(locationRequest, locationCallback, null /* Looper */) }
Java
@Override protected void onResume() { super.onResume(); if (mRequestingLocationUpdates) { startLocationUpdates(); } } private void startLocationUpdates() { mFusedLocationClient.requestLocationUpdates(mLocationRequest, mLocationCallback, null /* Looper */); }
Notice that the above code snippet refers to a boolean flag,
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
Save the State of the Activity.
Define the location update callback
The fused location provider invokes the
LocationCallback.onLocationResult()
callback method. The incoming argument contains a list Location
object containing the location's latitude and longitude. The following snippet
shows how to implement the
LocationCallback
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:
Kotlin
private lateinit var locationCallback: LocationCallback // ... override fun onCreate(savedInstanceState: Bundle?) { // ... locationCallback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult?) { locationResult ?: return for (location in locationResult.locations){ // Update UI with location data // ... } } } }
Java
private LocationCallback mLocationCallback; // ... @Override protected void onCreate(Bundle savedInstanceState) { // ... mLocationCallback = new LocationCallback() { @Override public void onLocationResult(LocationResult locationResult) { if (locationResult == null) { return; } for (Location location : locationResult.getLocations()) { // Update UI with location data // ... } }; }; }
Stop location updates
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
onPause()
method.
To stop location updates, call
removeLocationUpdates()
,
passing it a
LocationCallback
,
as shown in the following code sample:
Kotlin
override fun onPause() { super.onPause() stopLocationUpdates() } private fun stopLocationUpdates() { fusedLocationClient.removeLocationUpdates(locationCallback) }
Java
@Override protected void onPause() { super.onPause(); stopLocationUpdates(); } private void stopLocationUpdates() { mFusedLocationClient.removeLocationUpdates(mLocationCallback); }
Use a boolean, mRequestingLocationUpdates
, to track
whether location updates are currently turned on. In the activity's
onResume()
method, check
whether location updates are currently active, and activate them if not:
Kotlin
override fun onResume() { super.onResume() if (requestingLocationUpdates) startLocationUpdates() }
Java
@Override protected void onResume() { super.onResume(); if (mRequestingLocationUpdates) { startLocationUpdates(); } }
Save the state of the activity
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
Bundle
object.
The following code sample shows how to use the activity's
onSaveInstanceState()
callback to save the instance state:
Kotlin
override fun onSaveInstanceState(outState: Bundle?) { outState?.putBoolean(REQUESTING_LOCATION_UPDATES_KEY, requestingLocationUpdates) super.onSaveInstanceState(outState) }
Java
@Override protected void onSaveInstanceState(Bundle outState) { outState.putBoolean(REQUESTING_LOCATION_UPDATES_KEY, mRequestingLocationUpdates); // ... super.onSaveInstanceState(outState); }
Define an 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
onCreate()
method, as shown in the
following code sample:
Kotlin
override fun onCreate(savedInstanceState: Bundle?) { // ... updateValuesFromBundle(savedInstanceState) } private fun updateValuesFromBundle(savedInstanceState: Bundle?) { savedInstanceState ?: return // Update the value of requestingLocationUpdates from the Bundle. if (savedInstanceState.keySet().contains(REQUESTING_LOCATION_UPDATES_KEY)) { requestingLocationUpdates = savedInstanceState.getBoolean( REQUESTING_LOCATION_UPDATES_KEY) } // ... // Update UI to match restored state updateUI() }
Java
@Override public void onCreate(Bundle savedInstanceState) { // ... updateValuesFromBundle(savedInstanceState); } private void updateValuesFromBundle(Bundle savedInstanceState) { if (savedInstanceState == null) { return; } // Update the value of mRequestingLocationUpdates from the Bundle. if (savedInstanceState.keySet().contains(REQUESTING_LOCATION_UPDATES_KEY)) { mRequestingLocationUpdates = savedInstanceState.getBoolean( REQUESTING_LOCATION_UPDATES_KEY); } // ... // Update UI to match restored state updateUI(); }
For more about saving instance state, see the Android Activity class reference.
Note: For a more persistent storage, you can
store the user's preferences in your app's
SharedPreferences
. Set the shared preference in
your activity's onPause()
method, and
retrieve the preference in onResume()
.
For more information about saving preferences, read
Saving
Key-Value Sets.
The next lesson, Display a location address, shows you how to display the street address for a given location.