Howto cleanup location listeners in activities properly

Question

I have an Activity that implements LocationListener.

public class MyActivity extends MapActivity  implements LocationListener

In my activity, I register a locationlistener in the onCreate()

lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, minTime, distance, this);

In the onDestroy method, I'm removing the registration for my locationlistener.

@Override
protected void onDestroy() {
    Utils.addDebugMsg(this,"onDestroy");
    lm.removeUpdates(this);
    super.onDestroy();
}

In my application, I can change the minTime and distance, so I re-initialize my listener like this :

private void initializeGpsListener() {
    lm.removeUpdates(this);
    lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, minTime, distance, this);
}

For debugging purposes, I write something to the screen whenever a provider is enabled (in this case GPS).

    @Override
    public void onProviderEnabled(String provider) {
        Utils.addDebugMsg(this,"onProviderEnabled : " + provider);
    }

What I noticed is that sometimes, multiple instances of my activity (or locationlistener) are "kept around". Each time I turn the GPS provider on, instead of seeing 1 statement "onProviderEnabled : GPS", I see several different instances of my Activity printing this line (all at the same time).

How do I clean up these listeners ( = my activities), and make sure that only 1 remains active throughout the application.

Answer 1

The Activity implemented OnSharedPreferenceChangeListener.

During onCreate, the activity was registered as a PreferenceChangelistener, but not unregistered in the onDestroy().

As such, even after the activity was destroyed, there was still a reference to the activity, causing the duplicate messages.