为什么Android Beacon Library DidRangeBeanConsistinRegion有时会触发两次？

Question

这是一个关于Android Beacon库的问题。

应用程序使用BootstrapNotifier连续进行后台扫描
一旦检测到匹配的信标（即触发didEnterRegion），此后台扫描将被禁用，并启动开始对信标进行测距的前台服务。

（你可以参考这篇文章了解更多背景）

对于这个原子测试项目，您也可以参考这个存储库。

BeaconApplication负责连续的背景扫描
selfbeacervice负责主动前景测距。

（如果您手头有一个信标，并且想要构建和测试，则需要将标识符过滤器更改为null或您自己的标识符。）

有时（我说有时是因为我不知道如何100%复制），在selfbeacervice中，didrangebeaconregion会同时触发两次，但我只配置了一个区域。

下面是记录双触发器的日志
请注意，我已将扫描间隔设置为4秒。

03-07 10:46:31.811 (...) I/selfBeacon: Bootstrap didEnterRegion
03-07 10:46:31.812 (...) I/BeaconService: stop monitoring received
03-07 10:46:31.820 (...) I/selfBeacon: Service start commanded
03-07 10:46:31.831 (...) I/BeaconService: unbinding
03-07 10:46:31.832 (...) E/BeaconService: onDestroy()
03-07 10:46:31.834 (...) I/BeaconService: onDestroy called.  stopping scanning
03-07 10:46:31.838 (...) I/selfBeaconService: onCreate
03-07 10:46:31.839 (...) I/selfBeaconService: onStartCommand
03-07 10:46:31.929 (...) I/CycledLeScanner: This is Android 5.0.  We are using new scanning APIs
03-07 10:46:31.951 (...) I/BeaconService: beaconService version 2.13.1 is starting up on the main process
03-07 10:46:31.954 (...) W/ModelSpecificDistanceCalculator: App has no android.permission.INTERNET permission.  Cannot check for distance model updates
03-07 10:46:31.958 (...) W/ModelSpecificDistanceCalculator: Cannot find match for this device.  Using default
03-07 10:46:31.959 (...) W/ModelSpecificDistanceCalculator: Cannot find match for this device.  Using default
03-07 10:46:31.960 (...) I/BeaconService: binding
03-07 10:46:31.979 (...) I/selfBeaconService: onBeaconServiceConnect
03-07 10:46:31.980 (...) I/BeaconService: start ranging received
03-07 10:46:32.168 (...) I/art: Do partial code cache collection, code=10KB, data=24KB
03-07 10:46:32.169 (...) I/art: After code cache collection, code=10KB, data=24KB
03-07 10:46:32.169 (...) I/art: Increasing code cache capacity to 128KB
03-07 10:46:33.065 (...) I/ScanHelper: Non-distinct packets detected in a single scan.  Restarting scans unecessary.
03-07 10:46:33.106 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 3.4581850922412523 meters away.
03-07 10:46:36.726 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 3.4581850922412523 meters away.
03-07 10:46:40.726 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 3.6056118574381157 meters away.
03-07 10:46:41.285 (...) I/art: Debugger is no longer active
03-07 10:46:41.285 (...) I/art: Starting a blocking GC Instrumentation
03-07 10:46:42.392 (...) I/CycledLeScanner: This is Android 5.0.  We are using new scanning APIs
03-07 10:46:42.401 (...) I/ScanJob: Using immediateScanJobId from manifest: 208352939
03-07 10:46:42.401 (...) I/ScanJob: Running immediate scan job: instance is org.altbeacon.beacon.service.ScanJob@398f59c
03-07 10:46:42.402 (...) I/ScanJob: scanJob version 2.13.1 is starting up on the main process
03-07 10:46:42.402 (...) W/ModelSpecificDistanceCalculator: App has no android.permission.INTERNET permission.  Cannot check for distance model updates
03-07 10:46:42.404 (...) W/ModelSpecificDistanceCalculator: Cannot find match for this device.  Using default
03-07 10:46:42.404 (...) W/ModelSpecificDistanceCalculator: Cannot find match for this device.  Using default
03-07 10:46:42.409 (...) I/ScanJob: Scan job running for 300000 millis
03-07 10:46:43.528 (...) I/ScanHelper: Non-distinct packets detected in a single scan.  Restarting scans unecessary.
03-07 10:46:44.434 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 2.92768959654115 meters away.
03-07 10:46:44.727 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 3.4996718323492226 meters away.
03-07 10:46:46.451 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 3.181513412080198 meters away.
03-07 10:46:48.737 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 4.135957968665044 meters away.
03-07 10:46:48.743 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 3.4581850922412523 meters away.
03-07 10:46:52.732 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 7.408179588037119 meters away.
03-07 10:46:52.735 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 11.306160864298167 meters away.
03-07 10:46:56.736 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 5.632619096507348 meters away.
03-07 10:46:56.740 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 9.280517536034091 meters away.
03-07 10:47:00.728 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 9.280517536034091 meters away.
03-07 10:47:00.733 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 9.280517536034091 meters away.
03-07 10:47:04.729 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 8.917299181373306 meters away.
03-07 10:47:04.733 (...) I/selfBeaconService: didRangeBeaconsInRegion, the closest beacon is about 8.917299181373306 meters away.

正如您从10:46:33到10:46:40所看到的，它以4秒的间隔正常工作。在那之后，突然出现了一堆日志消息，看起来Android Beacon Library的某个东西（比如ScanJob）重启了
从那时起，10:46:44的回调每4秒触发两次。

所以问题是...发生了什么，或者为什么？

Answer 1

快速上下文总结：本项目是一个案例，作者试图通过在检测到信标时启动前台服务来优化Android 8上的不间断测距。当未检测到信标时，将在Android 8上使用默认的作业调度程序扫描。

根据日志，似乎是在前台服务启动常量范围后进行的摘录。然后，作业调度器启动，并在服务已经扫描的同时启动了一个ScanJob。这可能会产生双重回调，因为两个不同的线程同时执行循环扫描，并向同一委托报告范围结果。因此，该应用程序会得到两次回调。

这里的根本问题是，如果计划的作业用于扫描，则调用beaconManager。解除绑定（…） 不会取消计划以前计划的作业。库应该这样做，但从版本2.31起它就不这样做了。1.这将是图书馆需要解决的一个新问题。我在这里记录了一个问题

在此期间，可以手动取消作业。（注意：这使用私有库API，因此可能会在将来的版本中中断。在库中修复问题之前，最好暂时使用此类代码。）

有了上述警告，您应该能够在使用以下命令解除绑定后手动取消作业：

JobScheduler jobScheduler = (JobScheduler) 
  context.getSystemService(Context.JOB_SCHEDULER_SERVICE);
jobScheduler.cancel(ScanJob.getImmediateScanJobId(context));
jobScheduler.cancel(ScanJob.getPeriodicScanJobId(context));