杂记：解决Android扫描BLE设备名称不刷新问题

背景

个人开发过一种BLE设备有这样一种需求：当设备处于状态A时，广播设备名称A；处于状态B时，广播设备名称B。

问题

我们发现，当Android在进行Ble扫描的时候，扫描回调函数onScanResult中获取的设备名称并未随设备实时改变。

但是当使用nrfConnect进行扫描时，却发现设备广播名称确实是实时改变的。

原因

我们使用如下代码获取BLE设备名称，然而此时device.getName()中的名称是系统缓存的数据，而非实时的广播数据，要想获取实时的设备名称，必须自行解码实时广播数据。

    private ScanCallback mScanCallback = new ScanCallback() {
         @Override
         public void onScanResult(int callbackType, ScanResult result) {

             BluetoothDevice device = result.getDevice();
             if(null != device && null != device.getName()) {
                  Log.d("test", device.getName()); // not the real name
             }
         }

         @Override
         public void onScanFailed(int errorCode) {
               super.onScanFailed(errorCode);
         }

     };

解决

通过分析BLE广播包协议，自行解码出设备名称。

      private ScanCallback mScanCallback = new ScanCallback() {
           @Override
           public void onScanResult(int callbackType, ScanResult result) {

               BluetoothDevice device = result.getDevice();
               if(null != device && null != device.getScanRecord().getBytes()) {
                    byte[] scanRecord = device.getScanRecord().getBytes(); // advertised data
                    String realName = parseDeviceName(scanRecord);
               }
           }

          @Override
          public void onScanFailed(int errorCode) {
                super.onScanFailed(errorCode);
          }

      };

     // return name String(successful) or null(failed)
       public static String parseDeviceName(byte[] scanRecord) {
         String ret = null;
         if(null == scanRecord) {
             return ret;
         }

         ByteBuffer buffer = ByteBuffer.wrap(scanRecord).order(ByteOrder.LITTLE_ENDIAN);
         while (buffer.remaining() > 2) {
             byte length = buffer.get();
             if (length == 0)
                 break;

             byte type = buffer.get();
             length -= 1;
             switch (type) {
                 case 0x01: // Flags
                     buffer.get(); // flags
                     length--;
                     break;
                 case 0x02: // Partial list of 16-bit UUIDs
                 case 0x03: // Complete list of 16-bit UUIDs
                 case 0x14: // List of 16-bit Service Solicitation UUIDs
                     while (length >= 2) {
                         buffer.getShort();
                         length -= 2;
                     }
                     break;
                 case 0x04: // Partial list of 32 bit service UUIDs
                 case 0x05: // Complete list of 32 bit service UUIDs
                     while (length >= 4) {
                         buffer.getInt();
                         length -= 4;
                     }
                     break;
                 case 0x06: // Partial list of 128-bit UUIDs
                 case 0x07: // Complete list of 128-bit UUIDs
                 case 0x15: // List of 128-bit Service Solicitation UUIDs
                     while (length >= 16) {
                         long lsb = buffer.getLong();
                         long msb = buffer.getLong();
                         length -= 16;
                     }
                     break;
                 case 0x08: // Short local device name
                 case 0x09: // Complete local device name
                     byte sb[] = new byte[length];
                     buffer.get(sb, 0, length);
                     length = 0;
                     ret = new String(sb).trim();
                     return ret;
                 case (byte) 0xFF: // Manufacturer Specific Data
                     buffer.getShort();
                     length -= 2;
                     break;
                 default: // skip
                     break;
             }
             if (length > 0) {
                 buffer.position(buffer.position() + length);
             }
         }
         return ret;
     }

参考资料：

https://www.race604.com/ble-advertising/