为什么蓝牙低功耗扫描仪需要重新启动

Question

我注意到在 ble 扫描器的几个实现中，扫描在给定时间段后停止并再次开始，例如每 20 秒一次。

例如，这里有一个扫描程序类在单独的线程中启动扫描程序。您可以在 start() 方法中看到线程进入睡眠状态一段时间，然后停止并重新启动扫描程序：

public class BleScanner extends Thread {
    private final BluetoothAdapter bluetoothAdapter;
    private final BluetoothAdapter.LeScanCallback mLeScanCallback;
    private volatile boolean isScanning = false;
    public BleScanner(BluetoothAdapter adapter, BluetoothAdapter.LeScanCallback callback) {
        bluetoothAdapter = adapter;
        mLeScanCallback = callback;
    }
    public boolean isScanning() {
        return isScanning;
    }
    public void startScanning() {
        synchronized (this) {
            isScanning = true;
            start();
        }
    }
    public void stopScanning() {
        synchronized (this) {
            isScanning = false;
            bluetoothAdapter.stopLeScan(mLeScanCallback);
        }
    }
    @Override
    public void run() {
        try {
            // Thread goes into an infinite loop
            while (true) {
                synchronized (this) {
                    // If there is not currently a scan in progress, start one
                    if (!isScanning) break;
                    bluetoothAdapter.startLeScan(mLeScanCallback);
                }
                sleep(Constants.SCAN_PERIOD); // Thread sleeps before stopping the scan
                // stop scan
                synchronized (this) {
                    bluetoothAdapter.stopLeScan(mLeScanCallback);
                }
                // restart scan on next iteration of infinite while loop
            }
        } catch (InterruptedException ignore) {

        } finally { // Just in case there is an error, the scan will be stopped
            bluetoothAdapter.stopLeScan(mLeScanCallback);
            // The finally block always executes when the try block exits. This ensures that the
            // finally block is executed even if an unexpected exception occurs.
        }
    }
}

停止和重新启动扫描仪有什么好处吗？为什么不让扫描永久继续呢？

Answer 1

有优点。在某些设备上，每次扫描只会看到一次来自设备的播发。在某些广告上，您会看到所有广告。此外，重新启动扫描可以清理一些低级内容，并且通常比始终保持扫描程序处于活动状态要好。