Android Beacon Library - Background scanning

Question

I use the Android Beacon Library to scan Eddystone beacons with my phone. The application is properly running in the foreground.

Now, I want to detect Eddytone beacons in the background mode, but the example in the website of the library doesn't run on my application.

In my case, I have an activity for the UI and a separate Service for the foreground beacons detection.

I have exactly the same code of the example and the launchMode of my activity is "singleInstance".

Here is my code:

public class Background extends Application implements BootstrapNotifier{

    private static final String TAG = "Background";
    private RegionBootstrap regionBootstrap;

    @Override
    public void onCreate() {
        super.onCreate();
        Log.e(TAG, "App started up");
        BeaconManager beaconManager = BeaconManager.getInstanceForApplication(this);
        beaconManager.getBeaconParsers().add(new BeaconParser().setBeaconLayout(BeaconParser.EDDYSTONE_UID_LAYOUT));
        beaconManager.setBackgroundScanPeriod(1100L);
        beaconManager.setBackgroundBetweenScanPeriod(5000);
        Region region = new Region("all", null, null, null);
        regionBootstrap = new RegionBootstrap(this, region);
    }

    @Override
    public void didDetermineStateForRegion(int arg0, Region arg1) {
        // Don't care
    }

    @Override
    public void didEnterRegion(Region arg0) {
        Log.e(TAG, "Got a didEnterRegion call");
        regionBootstrap.disable();
        Intent intent = new Intent(this, MainActivity.class);
        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        this.startActivity(intent);
    }

    @Override
    public void didExitRegion(Region arg0) {
        // Don't care
    }
}

Am I missing anything? Or due to my separate service, this is not the proper method?

Thank you for your help.

Answer 1

If your app is "killed" of course you will not scan, because your App object doesn't exist at all.

What you need is use foreground service which runs all the time in background. Also you need to consider restart that service when device was restarted.

Answer 2

It is important to understand two things about how the Android Beacon Library works in this case:

1. When you swipe an app of the screen, it kills the process. The Android Beacon Library will attempt to restart its lightweight scanning service (and your application in the background) within 5 minutes of this happening. When it does, it will be a new process, so you will still see the same one as DEAD in Android Studio, but a new one should appear in the pull down menu.

2. The library persistently tracks region state for cases like this. So if you were already inside the region when you killed the app, you won't get a second didEnterRegion call when it starts back up. An easier way to test what is going on is to put a log line inside didDetermineStateForRegion, which gets called when the app starts back up regardless of the state.

There are a small percentage of Android devices that have non-standard task switchers that kill apps in a way that do not allow them to restart. In the unlikely event that you have one of these devices, the above won't work. To find out for sure, I would do this:

1. Add a new log line in didDetermineStateForRegion

2. On the command line, run adb logcat | grep Background to look for all log lines from your application, even after it restarts with a different process id.

3. Run your app and verify you see log output.

4. Kill your app.

5. Wait five minutes while watching the log output. Do you see App started up or the log line you added for didDetermineStateForRegion?

EDIT: Based on the log output provided in a link in the comments, I see that the app is running as process id 6863 detecting beacons for awhile:

03-28 14:31:17.540  6863  6863 E Background: App started up
...
03-28 14:31:18.196  6863  6935 E Background: Got a didEnterRegion call
...
03-28 14:31:23.550  6863  6863 E MainActivity: Beacons received

Then these entries appear:

03-28 14:31:24.932   928  1913 I MediaProcessHandler: processOp opType: 1, uid: 10138, pid: 6863
03-28 14:31:24.932   928  1913 W MediaProcessHandler: remove target not exist, maybe the UI process: uid: 10138, pid: 6863

It appears that a class called MediaProcessHandler in this non-standard Android OS flavor is killing the process at the time above. The Android Beacon Library uses an AlarmManager to restart scanning 5 minutes after the last scan in such a case, which should have gone off at 14:36:23 to resume scanning. Unfortunately, the log ends at 03-28 14:33:28.553, so I can't tell if this happened as designed.