active 和 passive 扫描之间的区别在于 active 扫描向广告商请求 SCAN_RESPONSE 包。这是通过在检测到广告后发送SCAN_REQUEST paket 来完成的。两者的信息（有效负载）都将在设备找到回调的scanRecord 参数中。
来自core spec：
设备可以使用主动扫描来获取有关设备的更多信息
这对于填充用户界面可能很有用。主动扫描涉及更多
链接层广告消息。
因此，对于任何用例，这两种扫描类型之间都没有必要区分。
但如果您想在后台收听广告，那么您需要自己创建一个Service - 没有内置功能（从 Android 4.4 开始）。
以后台扫描为例。但扫描将在您的应用被系统终止（或被用户停止）时结束。
通过 AlarmManager 启动 PendingIntent（在您的应用程序中的任何位置，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);
BleScan 服务
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();
}
}
常量只是分配意图动作和额外名称的字符串。还有另一个首选项存储存储扫描阶段应该多长时间...您可以根据需要轻松替换它。
然后您必须使用与上述操作名称匹配的意图过滤器注册广播接收器（BleServiceConstants.ACTION_DEVICE_DISCOVERED）
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
}
}