有什么方法可以在不连接的情况下监控发现的 BLE 外围设备？

Question

如果发现的 BLE 外围设备移出范围或以其他方式消失在视线之外，是否有任何方法可以收到通知？我正在使用 rxBleClient.scanBleDevices() 构建广告区域中的设备列表，但在将此列表发送到主应用程序之前，我想确保所有设备仍然可以访问。这样做的最佳方法是什么？

Answer 1

您可以创建一个 Transformer 来收集扫描的设备并发出一个列表，该列表会保持最新，具体取决于最近看到设备的时间。

Answer 2

香草 Android 扫描 API 允许扫描具有以下回调类型的 BLE 设备：

/**
 * A result callback is only triggered for the first advertisement packet received that matches
 * the filter criteria.
 */
public static final int CALLBACK_TYPE_FIRST_MATCH = 2;

/**
 * Receive a callback when advertisements are no longer received from a device that has been
 * previously reported by a first match callback.
 */
public static final int CALLBACK_TYPE_MATCH_LOST = 4;

相同的 API 可通过 RxBleClient.scanBleDevices(ScanSettings, ScanFilter...)

获得

CALLBACK_TYPE_FIRST_MATCH 和 CALLBACK_TYPE_MATCH_LOST 是可以放入 ScanSettings 的标志。

触发 CALLBACK_TYPE_MATCH_LOST 的超时时间约为 10 秒。这可能表示某个特定设备已不在 range/available。

Answer 3

罗伯特，这可能不是您所期望的，但请将其作为示例。我的 Transformer 每当更改时都会发出一个项目列表，这可能是因为来自扫描仪的更新或驱逐发生（每秒检查一次）。

class RollingPairableDeviceReducer(
        private val systemTime: SystemTime,
        private val evictionTimeSeconds: Long,
        private val pairableDeviceFactory: PairableDeviceFactory
) : Observable.Transformer<ScannedDevice, List<PairableDevice>> {
    override fun call(source: Observable<ScannedDevice>): Observable<List<PairableDevice>> {
        val accumulator: MutableSet<PairableDevice> = Collections.synchronizedSet(mutableSetOf())
        return source
                .map { createPairableDevice(it) }
                .map { pairableDevice ->
                    val added = updateOrAddDevice(accumulator, pairableDevice)
                    val removed = removeOldDevices(accumulator)
                    added || removed
                }
                .mergeWith(checkEvictionEverySecond(accumulator))
                .filter { addedOrRemoved -> addedOrRemoved == true }
                .map { accumulator.toList() }
    }

    private fun createPairableDevice(scannedDevice: ScannedDevice)
            = pairableDeviceFactory.create(scannedDevice)

    private fun updateOrAddDevice(accumulator: MutableSet<PairableDevice>, emittedItem: PairableDevice): Boolean {
        val existingPairableDevice = accumulator.find { it.deviceIdentifier.hardwareId == emittedItem.deviceIdentifier.hardwareId }
        return if (existingPairableDevice != null) {
            accumulator.remove(existingPairableDevice)
            existingPairableDevice.updateWith(emittedItem)
            accumulator.add(existingPairableDevice)
            false
        } else {
            accumulator.add(emittedItem)
            true
        }
    }

    private fun checkEvictionEverySecond(collector: MutableSet<PairableDevice>): Observable<Boolean>
            = Observable.interval(1, TimeUnit.SECONDS)
            .map { removeOldDevices(collector) }

    private fun removeOldDevices(accumulator: MutableSet<PairableDevice>): Boolean {
        val currentTimeInMillis = systemTime.currentTimeInMillis()
        val evictionTimeMillis = TimeUnit.SECONDS.toMillis(evictionTimeSeconds)
        return accumulator.removeAll { (currentTimeInMillis - it.lastSeenTime) >= evictionTimeMillis }
    }
}

有什么方法可以在不连接的情况下监控发现的 BLE 外围设备？

Any way to monitor discovered BLE peripherals without connecting?

android

bluetooth-lowenergy

rxandroidble