Locking screen of Android phone results in several subsequent onPause/onResume events

Question

I encountered this somewhat strange behavior while developing on Android and during my googling the only answer I could find was that this is by design and that I should not care about it.

My application fetches location data while active, and I was about to implement a way to preserve battery by stopping location updates when the onPause event is called, and later resume fetching when the onResume event is called.

While debugging I noticed this strange behavior when locking the phone, onPause->onResume get called one after another three or more times and then end with a onStop event. The only answer I where able to find was like: that's how android works, nevermind.

I guess I'm curious, can someone explain me the need to stop and resume a simple sub-activity several times? Doesn't that consume more battery, especially for larger activities that have serious code in onResume? Is there a way to prevent this from happening? I would be happy just by knowing that at least my code in those events doesn't get called, maybe with a if{} block preventing unnecessary CPU cycles.

Any insight is greatly appreciated!

Abnormal

Answer 1

You have to register broadcast receiver for handling "Screen Time Out" and "Screen Lock" events.

You just stop your data retrieving. Sample code:

public class ScreenReceiver extends BroadcastReceiver {     

        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(Intent.ACTION_SCREEN_OFF)) {
                //screen locked, do here 
            } else if (intent.getAction().equals(Intent.ACTION_SCREEN_ON)) {
                //screen unlocked, do something here
            }
        }

}

You need to register broadcast receiver for this ScreenReceiver class to the androidMenifest.xml

Rebhun

Thank you, that will probably do. Actually I was looking for more details on why this is happening, but probably I'm asking too much. – Abnormal

Answer 2

I recently ran into the same issue and was able to stop it from happening by playing with Config changes for the activity in the manifest file. I believe that when a user locks a device, a few things can happen: The orientation can change, the screen size can change (if navigation or notification bars disappear), etc. and that causes Android to rebuild all activities & fragments. I ended up selecting a lot of the options in Config changes and it stopped calling onResume after onPause.

Caucasian