AltBeacon - background scan configuration - beacon

Question

Sorry for my English :)
I have no idea how configure scanner to work properly in background (using ScanJob). I noticed that if the ScanJob starts more than 15 minutes after the previous scan is finished, a passive scan occurs even though there are beacons nearby. The reason for this is that the max age of the region is set to 15 minutes and the region is not restored after ScanJob starts. For now, I do so that after the scanner returns the results, I check if the list from monitoring regions is not empty and if it is, I do
if(beaconManager.monitoredRegions.isEmpty()) {
beaconManager.startRangingBeacons (region)
beaconManager.startMonitoring (region)
}
to set the region again. If I do not do this, passive scan starts every ScanJob stops .
If I invoke
beaconManager.startRangingBeacons (region)
beaconManager.startMonitoring (region)
each time if application starts then ScanJob is canceled immediately.
I wonder if there is any pattern to the background scan setup?
Maybe just remove condition in MonitoringStatus class?
if (millisSinceLastMonitor> MAX_STATUS_PRESERVATION_FILE_AGE_TO_RESTORE_SECS * 1000) {
LogManager.d (TAG, "Not restoring monitoring state because it was recorded too many milliseconds ago:" + millisSinceLastMonitor);
}

Answer 1

The scan job strategy is the default way the Android Beacon Library operates. It uses Android scheduled jobs to schedule scans and requires no configuration:
val beaconManager = BeaconManager.getInstanceForApplication(this)
val region = Region("all-beacons-region", null, null, beaconManager.startMonitoring(region)
beaconManager.startRangingBeacons(region)
In the foreground, scanning is constant and ranging callbacks come every ~1 sec.
In the background, scans are scheduled only once every ~15 minutes due to Android 8+ job scheduling limitations, so ranging callbacks come at that frequency. It is not designed for constant background scanning.
For constant background scanning you may configure the library to use a foreground service or the intent scan strategy.

Answer 2

I've wrote an simple application.
App: Aplication looks like this:
class App: Application(), MonitorNotifier {
val beaconManager by lazy { BeaconManager.getInstanceForApplication(this) }
val parser: BeaconParser =
BeaconParser().setBeaconLayout("m:2-3=0215,i:4-19,i:20-21,i:22-23,p:24-24")
override fun onCreate() {
BeaconManager.setDebug(true)
super.onCreate()
beaconManager.beaconParsers.add(parser)
beaconManager.addMonitorNotifier(this)
beaconManager.addRangeNotifier { mutableCollection: MutableCollection<Beacon>, region: Region ->
}
}
override fun didEnterRegion(region: Region?) {
}
override fun didExitRegion(region: Region?) {
}
override fun didDetermineStateForRegion(state: Int, region: Region?) {
}
}
MainActivity looks like this:
class MainActivity : AppCompatActivity() {
val region = Region("all-beacons-region", null, null, null)
val beaconManager by lazy { BeaconManager.getInstanceForApplication(this) }
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
override fun onResume() {
super.onResume()
beaconManager.startRangingBeacons(region)
beaconManager.startMonitoring(region)
}
}
in this app configuration, two cases are possible with the assumption that there are beacons nearby
case 1. ScanJob has been started up to 15 minutes after the last scan. After finishing work, you can see in the logs
ScanJob: Checking to see if we need to start a passive scan
ScanJob: We are inside a beacon region. We will not scan between cycles.
and that is correct behavior
case 2. ScanJob has been started more than 15 minutes after the last scan. After finishing work, you will see in the logs:
ScanJob: Checking to see if we need to start a passive scan
it means, the passive scan has started. After a while, StartupBroadcastReceiver is triggered with the results of the passive scan. ScanJob starts to process the passive scan results. After finishing work, you will see in the logs:
ScanJob: Checking to see if we need to start a passive scan
it means, the passive scan has been started again and after a while the StartupBroadcastRetuver will be triggered again with the results of the passive scan. And so it will be over and over again for a while
when you start MainActivity again and call
beaconManager.startRangingBeacons(region)
beaconManager.startMonitoring(region)
In my opinion it is caused by the fact that monitoring state is not restored after 15 minutes from the last scan in the MonitoringStatus class (condition below)
else if (millisSinceLastMonitor > MAX_STATUS_PRESERVATION_FILE_AGE_TO_RESTORE_SECS * 1000) {
LogManager.d(TAG, "Not restoring monitoring state because it was recorded too many milliseconds ago: "+millisSinceLastMonitor);
}
and after the scan is complete, the method is called
private void startPassiveScanIfNeeded() {
if (mScanState != null) {
LogManager.d(TAG, "Checking to see if we need to start a passive scan");
boolean insideAnyRegion = mScanState.getMonitoringStatus().insideAnyRegion();
if (insideAnyRegion) {
// TODO: Set up a scan filter for not detecting a beacon pattern
LogManager.i(TAG, "We are inside a beacon region. We will not scan between cycles.");
}
else {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
if (mScanHelper != null) {
mScanHelper.startAndroidOBackgroundScan(mScanState.getBeaconParsers());
}
}
else {
LogManager.d(TAG, "This is not Android O. No scanning between cycles when using ScanJob");
}
}
}
}
and insideAnyRegion is false because the monitoring state has not been restored, so passive scanning is started even though the beacons are nearby.
To get this case up pretty quickly, I suggest you set MAX_STATUS_PRESERVATION_FILE_AGE_TO_RESTORE_SECS = 1, then when ScanJob start for the first time, you will see what I mean.
The operating system does not always start ScanJob after 15 minutes

Answer 3

protected void updateMonitoringStatusTime(long time) {
File file = mContext.getFileStreamPath(STATUS_PRESERVATION_FILE_NAME);
file.setLastModified(time);
restoreMonitoringStatusIfNeeded();
}
private void restoreMonitoringStatusIfNeeded() {
if(mRegionsStatesMap.isEmpty()){
restoreMonitoringStatus();
}
}