Question

I’ve written a mapping application which uses GPS. Testing this on my phone (a Galaxy S2 running Gingerbread) I could see no change in behaviour according to the values set in the minTime and minDistance arguments – the GPS, as indicated by the system icon stayed on after a fix no matter what minTime was set.

Aware from the SDK docs, that these were only ‘hints’, I wrote my own battery conservation regime by delegating the GPS control to a service with an IBinder which the activities could bind to and receive location updates by means of a BroadcastReceiver. A ‘settings’ menu option activity set parameters (‘GPS sleep time’ and ‘required accuracy’ which would turn off the GPS in the service for the sleep time once the accuracy criterion was satisfied. For completeness I also passed in minTime and minDistance parameters, which based on my empirical evidence I assumed would be redundant. I did my best to explain the effect of these settings in one of the app’s help pages:

Now my phone has just been upgrade to to ICS, I do find that the minTime does affect the state of the GPS (at least as reflected by the satellite icon on the status bar). In fact it disappears for almost exactly the set time after a fix.

I’m now in a quandary as to what to expect from any particular device/OS version combination and how to adapt my app to cope. To try and resolve it I’ll ask two specific questions:

Has any developer observed such a change in behaviour in their device when changing from Gingerbread to ICS?

Is such a change documented anywhere?

All factually based answers will be appreciated.

UPDATE 3rd April – smallest code sample I can produce to demonstrate behaviour of device appended below

public class GPSParamTestActivity extends Activity implements LocationListener,
        GpsStatus.Listener {

    private LocationManager mLocMgr;
    private long mUpdatePeriod = 10000; // 10 seconds
    private TextView mLocTV,  mStatTV, mGPSStatTV; // 3 TextViews for o/p
    private boolean mStatColourToggle, mLocnColourToggle, mGPSStatColourToggle;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        // Layout at http://dl.dropbox.com/u/67134160/main.xml if needed
    }

    @Override
    protected void onResume() {
        super.onResume();
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
        mLocTV = (TextView) findViewById(R.id.locnTV);
        mStatTV = (TextView) findViewById(R.id.statusTV);
        mGPSStatTV = (TextView) findViewById(R.id.gpsStatusTV);
        mLocMgr = (LocationManager) getSystemService(LOCATION_SERVICE);
    }

    @Override
    protected void onPause() {
        mLocMgr.removeGpsStatusListener(this);
        mLocMgr.removeUpdates(this); // Don't leave GPS on 
        super.onPause();
    }

    @Override
    public void onGpsStatusChanged(int event) {// GpsStatus.Listener fires this one
        mGPSStatTV.setTextColor(mGPSStatColourToggle ? Color.RED : Color.BLUE);
        mGPSStatColourToggle = !mGPSStatColourToggle;
        String str = "";
        switch (event) {
            case GpsStatus.GPS_EVENT_SATELLITE_STATUS:
                str = "GPS_EVENT_SATELLITE_STATUS";
                break; 
            case GpsStatus.GPS_EVENT_FIRST_FIX:
                str = "GPS_EVENT_FIRST_FIX";
                break;
            case GpsStatus.GPS_EVENT_STARTED:
                str = "GPS_EVENT_STARTED";
                break;
            case GpsStatus.GPS_EVENT_STOPPED:
                str = "GPS_EVENT_STOPPED";
                break;
        }
        mGPSStatTV.setText(str);
    }

    @Override
    public void onLocationChanged(Location loc) {
        mLocTV.setTextColor(mLocnColourToggle ? Color.RED : Color.BLUE);
        mLocnColourToggle = !mLocnColourToggle;
        String str = null;
        NumberFormat formatter = new DecimalFormat("##0.000000");
        String fLat = formatter.format(loc.getLatitude());
        String fLon = formatter.format(loc.getLongitude());
        str = "Lat/Lon " + fLat + "/" + fLon;
        mLocTV.setText(str);
    }

    @Override public void onProviderDisabled(String provider) {}
    @Override public void onProviderEnabled(String provider) {}

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
        // This is never triggered on a Galaxy S2, G'bread or ICS
        mStatTV.setTextColor(mStatColourToggle ? Color.RED : Color.BLUE);
        mStatColourToggle = !mStatColourToggle;
        String str = "Status chg " + provider;
        switch (status) {
            case android.location.LocationProvider.OUT_OF_SERVICE:
                str += " OUT OF SERVICE";
                break;
            case android.location.LocationProvider.AVAILABLE:
                str += " AVAILABLE";
                break;
            case android.location.LocationProvider.TEMPORARILY_UNAVAILABLE:
                str += " TEMPORARILY UNAVAILABLE";
                break;
            default:
                str += " UNKNOWN STATUS";
        }
        mStatTV.setText(str);
    }

    public void myClickHandler(View target) {
        mLocMgr.removeGpsStatusListener(this); // stop all listeners
        mLocMgr.removeUpdates(this);           // by default 
        // 3 buttons for app control, set the listeners to here in the XML
        switch (target.getId()) {
            case R.id.stopGPSButton:
                break; // already done by default
            case R.id.tenSecStartButton:
                mLocMgr.addGpsStatusListener(this);
                mLocMgr.requestLocationUpdates(LocationManager.GPS_PROVIDER,
                        mUpdatePeriod, 0, (LocationListener) this);
                break;
            case R.id.zeroSecStartButton:
                mLocMgr.addGpsStatusListener(this);
                mLocMgr.requestLocationUpdates(LocationManager.GPS_PROVIDER,
                        0, 0, (LocationListener) this);
                break;
        }
    }
}

.

Answer 1

While it’s not a real answer this post may be interesting:

I believe I’ve narrowed down the problem to faulty capability
reporting from native code to the GpsLocationProvider in the Android
platform. In a custom AOSP build on the same Nexus S 4G, I hard-coded
values in the GpsLocationProvider to indicate that the native code was
NOT capable of handling GPS scheduling. Voila, the platform took over
and properly followed the minTime parameter (60 seconds in this case)
and delivered location updates to the app 60 seconds apart.
So, it seems to me that the native code is telling the platform “I can
handle GPS scheduling”, but then it doesn’t, resulting in a 1Hz update
rate no matter the minTime interval requested by the application.