Running GPS positioning in a background thread on Android

Question

I have curious problem, in my application, the GPS-positioning takes quite a long time (as it tends to do) and therefore I wanted to run it as its own thread while the user is making choices in other views.

My structure is that I have a "main" view that is always active in the background, then the user is shown a series of views in which he or she makes a few choices. In the end, the user is presented with a result based on the choices made and the current position. All of this works, but I wanted to move the GPS-bit to its own thread so that the user wouldn't have to wait for it to finish.

All of the user's choices and the GPS coordinates is stored in a singleton called CurrentLogEntry. All communication between the different parts of the program is performed through it.

I created a handleMessage(Message msg) override in the main view and then I implemented this function in Main.java:

void startGPSThread() {
    Thread t = new Thread() {

        LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);     
        boolean isDebug = CurrentLogEntry.getInstance().isDebug();

        // Define a listener that responds to location updates
        LocationListener locationListener  = new LocationListener() {

            public void onStatusChanged(String provider, int status, Bundle extras) {
                /* This is called when the GPS status changes */
                String tag = "onStatusChanged, ";
                switch (status) {
                    case LocationProvider.OUT_OF_SERVICE:
                        Log.w(tag, "Status Changed: Out of Service");
                        break;
                    case LocationProvider.TEMPORARILY_UNAVAILABLE:
                        Log.w(tag, "Status Changed: Temporarily Unavailable");
                        break;
                    case LocationProvider.AVAILABLE:
                        break;
                }
            }

            public void onProviderEnabled(String provider) {
            }

            public void onProviderDisabled(String provider) {
                // This is called if the GPS is disabled in settings.
                // Bring up the GPS settings
                Intent intent = new Intent(
                        android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                startActivity(intent);
            }

            public void onLocationChanged(Location location) {

                // Once a location has been received, ignore all other position
                // updates.
                locationManager.removeUpdates(locationListener);
                locationManager.removeUpdates(this);

                // Make sure that the received location is a valid one,
                // otherwise show a warning toast and hit "back".
                if (location == null) {
                    String warningString = "Location was unititialized!";

                    if (isDebug) {
                        Toast.makeText(getApplicationContext(),
                                warningString,
                                Toast.LENGTH_LONG).show();
                    }

                    KeyEvent kev = new KeyEvent(KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_BACK);
                    onKeyDown(KeyEvent.KEYCODE_BACK, kev);
                }

                CurrentLogEntry.getInstance().setUserLatitude(location.getLatitude());
                CurrentLogEntry.getInstance().setUserLongitude(location.getLongitude());

                //Send update to the main thread
                int result = 0;
                if (location.getLatitude() == 0 || location.getLongitude() == 0) {
                    result = -1;
                }

                messageHandler.sendMessage(Message.obtain(messageHandler, result));
            }
        };

        @Override
        public void run() {

            locationManager.requestLocationUpdates(
                    LocationManager.GPS_PROVIDER, 0, 0, locationListener);

            // Wait until a position has bee acquired.
            while(!CurrentLogEntry.getInstance().isReadyToCalculate()){
                try {
                    wait(250);
                } catch (InterruptedException ex) {
                    Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
    };

    t.start();
}

This function is called in Main.onCreate() .

Unfortunately, this doesn't work at all. The program crashes as soon as it reaches locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener); and that has me completely stumped.

Can anyone enlighten me as to why this won't run as a background thread? Also, do I really need the wait-polling at the end to ensure that the thread stays alive until it receives its data? The GPS bit worked just fine before I wanted to put it in a thread of its own, so what in the world am I doing wrong?

Answer 1

From what i understand you have to make the Thread a Looper thread in order to run Location Updates in the background...however i am still trying to figure this out myself...when i figure out how to do this i will post it.

Probably have the same error that i received, which is can't create handler in thread where Looper.prepare() has not been called

Hope you get it working bud

Answer 2

Check the this thread and specifically for this answer. They deal with the same subject, location, and the same problem, running it from a Thread loop.