Android BLE被动扫描

Question

我想在我的Android应用程序中被动地扫描BLE广告商。

但我找不到该怎么做。

• 根据蓝牙4.0内核规范，存在无源扫描模式。 卷6:核心系统封装低能控制器卷， D部分:4.1被动扫描 id=282159 “一种设备可以使用被动扫描来查找该地区的广告设备。”
• 此外，android有确定扫描类型的参数。(主动/被动) gap.c#555 Scan_type:主动扫描还是被动扫描
• 同时，iOS可以被动地扫描广告商。(遗憾的是，仅限于后台模式) http://lists.apple.com/archives/bluetooth-dev/2012/May/msg00041.html “当应用程序处于后台时，iOS执行被动扫描。”

但我找不到是否可以使用无源扫描模式。

问题：在Android上可以使用“被动扫描”吗？如果可能的话，如何使用这个特性？

Answer 1

active和passive扫描的不同之处在于，active扫描要求广告商提供SCAN_RESPONSE paket。这是通过在检测到广告后发送一个SCAN_REQUEST标记来完成的。两者的信息(有效载荷)都将在找到的回调设备的scanRecord参数中。

来自core spec

一个设备可以使用主动扫描来获得更多的信息，关于可能对填充用户界面有用的设备的。主动扫描涉及更多链接层广告消息。

因此，对于任何使用，没有必要在这两种扫描类型之间进行区别。

但是如果你想在后台收听广告，那么你需要自己创建一个Service --没有内置的功能(截至Android4.4)。

对于背景扫描，请以下面的例子为例。但是扫描会在你的应用程序被系统杀死(或者被用户停止)时结束。

通过PendingIntent启动AlarmManager (应用程序中的任何地方，必须至少运行一次才能启动服务.)

AlarmManager alarmMgr = (AlarmManager) getActivity().getSystemService(Context.ALARM_SERVICE);
Intent intent = new Intent(getActivity(), BleScanService.class);
PendingIntent scanIntent = PendingIntent.getService(getActivity(), 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
alarmMgr.setRepeating(AlarmManager.RTC_WAKEUP, SystemClock.elapsedRealtime(), intervalMillis, scanIntent);

BleScanService

public class BleScanService extends Service implements LeScanCallback {

private final static String TAG = BleScanService.class.getSimpleName();

private final IBinder mBinder = new LocalBinder();

private BluetoothManager mBluetoothManager;

private BluetoothAdapter mBluetoothAdapter;

public class LocalBinder extends Binder {
        public BleScanService getService() {
            return BleScanService.this;
        }
    }

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        return super.onUnbind(intent);
    }

    @Override
    public void onCreate() {
        super.onCreate();
        initialize();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        long timeToScan = preferences.scanLength().get();
        startScan(timeToScan);

        return super.onStartCommand(intent, flags, startId);
    }

    /**
     * Initializes a reference to the local bluetooth adapter.
     * 
     * @return Return true if the initialization is successful.
     */
    public boolean initialize() {
        // For API level 18 and above, get a reference to BluetoothAdapter
        // through
        // BluetoothManager.
        if (mBluetoothManager == null) {
            mBluetoothManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
            if (mBluetoothManager == null) {
                Log.e(TAG, "Unable to initialize BluetoothManager.");
                return false;
            }
        }

        if (mBluetoothAdapter == null) {
            mBluetoothAdapter = mBluetoothManager.getAdapter();
            if (mBluetoothAdapter == null) {
                Log.e(TAG, "Unable to obtain a BluetoothAdapter.");
                return false;
            }
        }

        Log.d(TAG, "Initialzed scanner.");
        return true;
    }

    /**
     * Checks if bluetooth is correctly set up.
     * 
     * @return
     */
    protected boolean isInitialized() {
        return mBluetoothManager != null && mBluetoothAdapter != null && mBluetoothAdapter.isEnabled();
    }

    /**
     * Checks if ble is ready and bluetooth is correctly setup.
     * 
     * @return
     */
    protected boolean isReady() {
        return isInitialized() && isBleReady();
    }

    /**
     * Checks if the device is ble ready.
     * 
     * @return
     */
    protected boolean isBleReady() {
        return getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE);
    }

    @Override
    public void onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord) {
        Log.d(TAG, "Found ble device " + device.getName() + " " + device.getAddress());
        broadcastOnDeviceFound(device, scanRecord);
    }

    /**
     * Broadcasts a message with the given device.
     * 
     * @param device
     * @param scanRecord 
     */
    protected void broadcastOnDeviceFound(final BluetoothDevice device, byte[] scanRecord) {
        assert device != null : "Device should not be null.";

        Intent intent = new Intent(BleServiceConstants.ACTION_DEVICE_DISCOVERED);
        intent.putExtra(BleServiceConstants.EXTRA_DEVICE_DISCOVERED_DEVICE, device);
        intent.putExtra(BleServiceConstants.EXTRA_DEVICE_DISCOVERED_SCAN_RECORD, scanRecord);
        sendBroadcast(intent);
    }

    /**
     * Starts the bluetooth low energy scan It scans at least the
     * delayStopTimeInMillis.
     * 
     * @param delayStopTimeInMillis
     *            the duration of the scan
     * @return <code>true</code> if the scan is successfully started.
     */
    public boolean startScan(long delayStopTimeInMillis) {
        if (!isReady())
            return false;

        if (preferences.shouldScan().get()) {
            if (delayStopTimeInMillis <= 0) {
                Log.w(TAG, "Did not start scanning with automatic stop delay time of " + delayStopTimeInMillis);
                return false;
            }

            Log.d(TAG, "Auto-Stop scan after " + delayStopTimeInMillis + " ms");
            getMainHandler().postDelayed(new Runnable() {

                @Override
                public void run() {
                    Log.d(TAG, "Stopped scan.");
                    stopScan();
                }
            }, delayStopTimeInMillis);
        }
        return startScan();
    }

    /**
     * @return an handler with the main (ui) looper.
     */
    private Handler getMainHandler() {
        return new Handler(getMainLooper());
    }

    /**
     * Starts the bluetooth low energy scan. It scans without time limit.
     * 
     * @return <code>true</code> if the scan is successfully started.
     */
    public boolean startScan() {
        if (!isReady())
            return false;

        if (preferences.shouldScan().get()) {
            if (mBluetoothAdapter != null) {
                Log.d(TAG, "Started scan.");
                return mBluetoothAdapter.startLeScan(this);
            } else {
                Log.d(TAG, "BluetoothAdapter is null.");
                return false;
            }
        }
        return false;
    }

    /**
     * Stops the bluetooth low energy scan.
     */
    public void stopScan() {
        if (!isReady())
            return;

        if (mBluetoothAdapter != null)
            mBluetoothAdapter.stopLeScan(this);
        else {
            Log.d(TAG, "BluetoothAdapter is null.");
        }
    }

    @Override
    public void onDestroy() {
        preferences.edit().shouldScan().put(false).apply();
        super.onDestroy();
    }
}

常量只是用来分发意图、动作和额外名称的字符串。还有另一个首选项存储，它存储扫描阶段应该多长时间，be...You可以轻松地替换它，满足您的需要。

然后，您必须使用与上述操作名称(BleServiceConstants.ACTION_DEVICE_DISCOVERED)匹配的意图筛选器注册广播接收者。

public class DeviceWatcher extends BroadcastReceiver {

  @Override
    public void onReceive(Context context, Intent intent) {
        BluetoothDevice device =  intent.getParcelableExtra(BleServiceConstants.EXTRA_DEVICE_DISCOVERED_DEVICE);

  // do anything with this information

  }
}

Answer 2

在AOSP回购中找到btif_gatt_client.c，编辑它，

替换

BTM_BleSetScanParams(p_cb->scan_interval, p_cb->scan_window, BTM_BLE_SCAN_MODE_ACTI);

使用

BTM_BleSetScanParams(p_cb->scan_interval, p_cb->scan_window, BTM_BLE_SCAN_MODE_PASS);

然后建立AOSP，将图像闪存到电话，然后被动扫描工作。