znat znat - 12 days ago 5
Android Question

Sending message to a Handler on a dead thread when getting a location from an IntentService

My app needs location fixes on regular basis, even when the phone is not awake.
To do this, I am using IntentService with the pattern generously provided by Commonsware.
https://github.com/commonsguy/cwac-wakeful

To get location fixes, I rely on the following code provided by a member called Fedor.
What is the simplest and most robust way to get the user's current location in Android?. I slightly modified it to return null instead of getting the last known location

They both work perfectly fine when not combined: I can get a location fix from Fedor's class in an Activity, and I can do some basic stuff ( like logging something) using Commonsware class.

The problem occurs when I am trying to get location fixes from the Commonsware's WakefulIntentService subclass. The LocationListeners do not react to locationUpdates and I get these warnings (I don't get yet the subtleties of threads, handlers, ...) . Can someone help me understand what the problem is? Thanks and I wish you all a very happy new year :)

12-31 14:09:33.664: W/MessageQueue(3264): Handler (android.location.LocationManager$ListenerTransport$1) {41403330} sending message to a Handler on a dead thread
12-31 14:09:33.664: W/MessageQueue(3264): java.lang.RuntimeException: Handler (android.location.LocationManager$ListenerTransport$1) {41403330} sending message to a Handler on a dead thread
12-31 14:09:33.664: W/MessageQueue(3264): at android.os.MessageQueue.enqueueMessage(MessageQueue.java:196)
12-31 14:09:33.664: W/MessageQueue(3264): at android.os.Handler.sendMessageAtTime(Handler.java:473)
12-31 14:09:33.664: W/MessageQueue(3264): at android.os.Handler.sendMessageDelayed(Handler.java:446)
12-31 14:09:33.664: W/MessageQueue(3264): at android.os.Handler.sendMessage(Handler.java:383)
12-31 14:09:33.664: W/MessageQueue(3264): at android.location.LocationManager$ListenerTransport.onLocationChanged(LocationManager.java:193)
12-31 14:09:33.664: W/MessageQueue(3264): at android.location.ILocationListener$Stub.onTransact(ILocationListener.java:58)
12-31 14:09:33.664: W/MessageQueue(3264): at android.os.Binder.execTransact(Binder.java:338)
12-31 14:09:33.664: W/MessageQueue(3264): at dalvik.system.NativeStart.run(Native Method)


This is my WakefulIntentService subclass:

public class AppService extends WakefulIntentService {
public static final String TAG = "AppService";
public AppService() {
super("AppService");
}

public LocationResult locationResult = new LocationResult() {
@Override
public void gotLocation(final Location location) {
if (location == null)
Log.d(TAG, "location could not be retrieved");
else
sendMessage(location);
}
};

@Override
protected void doWakefulWork(Intent intent) {
PhoneLocation myLocation;
myLocation = new PhoneLocation();
myLocation.getLocation(getApplicationContext(), locationResult);
}


And here a copy of Fedor's class (slightly modified: no need of GPS nor last known location)

public class PhoneLocation {
public static String TAG = "MyLocation";
Timer timer1;
LocationManager lm;
LocationResult locationResult;
boolean gps_enabled=false;
boolean network_enabled=false;

public boolean getLocation(Context context, LocationResult result)
{
//I use LocationResult callback class to pass location value from MyLocation to user code.
locationResult=result;
if(lm==null) lm = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);

//exceptions will be thrown if provider is not permitted.
try{gps_enabled=lm.isProviderEnabled(LocationManager.GPS_PROVIDER);}catch(Exception ex){}
try{network_enabled=lm.isProviderEnabled(LocationManager.NETWORK_PROVIDER);}catch(Exception ex){}

//don't start listeners if no provider is enabled
if(!gps_enabled && !network_enabled)
return false;

if(network_enabled) lm.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListenerNetwork);

timer1=new Timer();
timer1.schedule(new ReturnNullLocation(), 20000);
return true;
}

LocationListener locationListenerNetwork = new LocationListener() {
public void onLocationChanged(Location location) {
timer1.cancel();
locationResult.gotLocation(location);
lm.removeUpdates(this);
}
public void onProviderDisabled(String provider) {}
public void onProviderEnabled(String provider) {}
public void onStatusChanged(String provider, int status, Bundle extras) {}
};

class ReturnNullLocation extends TimerTask {
@Override
public void run() {
lm.removeUpdates(locationListenerNetwork);
locationResult.gotLocation(null);
}
}

public static abstract class LocationResult{
public abstract void gotLocation(Location location);

}


}

Answer

You cannot safely register listeners from an IntentService, as the IntentService goes away as soon as onHandleIntent() (a.k.a., doWakefulWork()) completes. Instead, you will need to use a regular service, plus handle details like timeouts (e.g., the user is in a basement and cannot get a GPS signal).

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