android - 使用 ScanSettings.SCAN_MODE_OPPORTUNISTIC '应用程序扫描太频繁'

Question

我注意到 Samsung S8、Android 7.0(更新。这也发生在 Android 7.0:Samsung S7、Nexus 5x)上的一个问题，它告诉(经过几次测试)应用扫描过于频繁:

08-14 12:44:20.693 25329-25329/com.my.app D/BluetoothAdapter: startLeScan(): null
08-14 12:44:20.695 25329-25329/com.my.app D/BluetoothAdapter: STATE_ON
08-14 12:44:20.696 25329-25329/com.my.app D/BluetoothAdapter: STATE_ON
08-14 12:44:20.698 25329-25329/com.my.app D/BluetoothLeScanner: Start Scan
08-14 12:44:20.699 25329-25329/com.my.app D/BluetoothAdapter: STATE_ON
08-14 12:44:20.700 25329-25329/com.my.app D/BluetoothAdapter: STATE_ON
08-14 12:44:20.700 25329-25329/com.my.app D/BluetoothAdapter: STATE_ON
08-14 12:44:20.701 25329-25329/com.my.app D/BluetoothAdapter: STATE_ON
08-14 12:44:20.703 4079-4093/? D/BtGatt.GattService: registerClient() - UUID=dbaafee1-caf1-4482-9025-b712f000eeab
08-14 12:44:20.807 4079-4204/? D/BtGatt.GattService: onClientRegistered() - UUID=dbaafee1-caf1-4482-9025-b712f000eeab, clientIf=5, status=0
08-14 12:44:20.808 25329-25342/com.my.app D/BluetoothLeScanner: onClientRegistered() - status=0 clientIf=5 mClientIf=0
08-14 12:44:20.809 4079-7185/? D/BtGatt.GattService: start scan with filters
08-14 12:44:20.811 4079-7185/? D/BtGatt.GattService: getScanSettings 
08-14 12:44:20.812 4079-7185/? D/BtGatt.GattService: Is it foreground application = true
08-14 12:44:20.812 4079-7185/? D/BtGatt.GattService: not a background application
08-14 12:44:20.817 4079-7185/? E/BtGatt.GattService: App 'com.my.app' is scanning too frequently

问题肯定在于那 6 个 STATE_ON 调用结果，这是未记录的 BLE 行为更改的一部分，在 DP4 发行说明中首次提到:

We’ve changed the BLE Scanning behavior starting in DP4. We’ll prevent applications from starting and stopping scans more than 5 times in 30 seconds. For long running scans, we’ll convert them into opportunistic scans.

即使我设置了:ScanSettings.setScanMode(ScanSettings.SCAN_MODE_OPPORTUNISTIC)，我也没有在 30 秒内完成 6 次扫描。

代码是:

List<ScanFilter> filters = new ArrayList<>();
ScanSettings scanSettings = new ScanSettings.Builder()
    .setScanMode(ScanSettings.SCAN_MODE_OPPORTUNISTIC)
    .build();
bluetoothAdapter.getBluetoothLeScanner().startScan(filters, scanSettings, recoderScanCallback);
//events from the log happen before this log is printed
Log.i("test", " started!");
return recoderScanCallback.scanResultObservable().map((ScanResult record) -> {
    //never gets here
    Log.i("test", " result!");
});

RecorderScanCallback 派生自 ScanCallback。我们无法使用 RxAndroidBle#rxBleClient.scanBleSettings(ScanSettings)，因为我们的代码即将卡住，我们使用的是 1.1.0 版本的 lib。

为什么 ScanSettings.setScanMode 不改变搜索结果？

Answer 1

Android 7 可在 30 秒内防止扫描开始-停止超过 5 次。不好的一面是，它不返回错误，而只是打印日志。该应用程序认为扫描已开始，但实际上并未从 ble 堆栈开始。它还将长时间运行的扫描转换为机会扫描，以防止滥用应用程序。长时间运行扫描的持续时间为 30 分钟。

这些更改未记录在案，在这篇文章中提到:https://blog.classycode.com/undocumented-android-7-ble-behavior-changes-d1a9bd87d983