نقل بيانات BLE

بعد الاتصال بخادم BLE GATT، يمكنك استخدام الاتصال لمعرفة الخدمات المتاحة على الجهاز، والاستعلام عن البيانات من الجهاز، وطلب الإشعارات عند تغيير إحدى خصائص GATT.

الاطّلاع على الخدمات

أول شيء يجب فعله عند الاتصال بخادم GATT على جهاز BLE هو اكتشاف الخدمة. ويوفّر ذلك معلومات حول الخدمات المتاحة على الجهاز البعيد بالإضافة إلى خصائص الخدمة وأوصافها. في المثال التالي، بعد اتصال الخدمة بالجهاز بنجاح (والمُشار إليه بالاستدعاء المناسب لوظيفة onConnectionStateChange() في BluetoothGattCallback)، ستبحث الدالة discoverServices() عن المعلومات من جهاز BLE.

يجب أن تلغي الخدمة دالة onServicesDiscovered() في BluetoothGattCallback. يتم استدعاء هذه الدالة عندما يسجّل الجهاز خدماته المتاحة.

class BluetoothLeService : Service() {

...

private val bluetoothGattCallback = object : BluetoothGattCallback() {
    override fun onConnectionStateChange(gatt: BluetoothGatt?, status: Int, newState: Int) {
        if (newState == BluetoothProfile.STATE_CONNECTED) {
            // successfully connected to the GATT Server
            broadcastUpdate(ACTION_GATT_CONNECTED)
            connectionState = STATE_CONNECTED
            // Attempts to discover services after successful connection.
            bluetoothGatt?.discoverServices()
        } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
            // disconnected from the GATT Server
            broadcastUpdate(ACTION_GATT_DISCONNECTED)
            connectionState = STATE_DISCONNECTED
        }
    }

    override fun onServicesDiscovered(gatt: BluetoothGatt?, status: Int) {
        if (status == BluetoothGatt.GATT_SUCCESS) {
            broadcastUpdate(ACTION_GATT_SERVICES_DISCOVERED)
        } else {
            Log.w(BluetoothService.TAG, "onServicesDiscovered received: $status")
        }
    }
}

...

companion object {
  const val ACTION_GATT_CONNECTED = "com.example.bluetooth.le.ACTION_GATT_CONNECTED"
  const val ACTION_GATT_DISCONNECTED =
              "com.example.bluetooth.le.ACTION_GATT_DISCONNECTED"
  const val ACTION_GATT_SERVICES_DISCOVERED =
              "com.example.bluetooth.le.ACTION_GATT_SERVICES_DISCOVERED"

  private const val STATE_DISCONNECTED = 0
  private const val STATE_CONNECTED = 2
}

class BluetoothService extends Service {

    public final static String ACTION_GATT_SERVICES_DISCOVERED =
            "com.example.bluetooth.le.ACTION_GATT_SERVICES_DISCOVERED";

    ...

    private final BluetoothGattCallback bluetoothGattCallback = new BluetoothGattCallback() {
        @Override
        public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
            if (newState == BluetoothProfile.STATE_CONNECTED) {
                // successfully connected to the GATT Server
                connectionState = STATE_CONNECTED;
                broadcastUpdate(ACTION_GATT_CONNECTED);
                // Attempts to discover services after successful connection.
                bluetoothGatt.discoverServices();
            } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
                // disconnected from the GATT Server
                connectionState = STATE_DISCONNECTED;
                broadcastUpdate(ACTION_GATT_DISCONNECTED);
            }
        }

        @Override
        public void onServicesDiscovered(BluetoothGatt gatt, int status) {
            if (status == BluetoothGatt.GATT_SUCCESS) {
                broadcastUpdate(ACTION_GATT_SERVICES_DISCOVERED);
            } else {
                Log.w(TAG, "onServicesDiscovered received: " + status);
            }
        }
    };
}

تستخدم الخدمة عمليات البث لإرسال إشعار بالنشاط. بعد اكتشاف الخدمات، يمكن للخدمة الاتصال بالرمز getServices() للحصول على البيانات التي تم الإبلاغ عنها.

class BluetoothLeService : Service() {

...

  fun getSupportedGattServices(): List<BluetoothGattService?>? {
      return bluetoothGatt?.services
  }
}

class BluetoothService extends Service {

...

    public List<BluetoothGattService> getSupportedGattServices() {
        if (bluetoothGatt == null) return null;
        return bluetoothGatt.getServices();
    }
}

ويمكن عندئذٍ استدعاء النشاط لهذه الدالة عندما تتلقّى هدف البث، مشيرًا إلى أنّ اكتشاف الخدمة قد اكتمل.

class DeviceControlActivity : AppCompatActivity() {

...

    private val gattUpdateReceiver: BroadcastReceiver = object : BroadcastReceiver() {
        override fun onReceive(context: Context, intent: Intent) {
            when (intent.action) {
                BluetoothLeService.ACTION_GATT_CONNECTED -> {
                    connected = true
                    updateConnectionState(R.string.connected)
                }
                BluetoothLeService.ACTION_GATT_DISCONNECTED -> {
                    connected = false
                    updateConnectionState(R.string.disconnected)
                        }
                BluetoothLeService.ACTION_GATT_SERVICES_DISCOVERED -> {
                    // Show all the supported services and characteristics on the user interface.
                    displayGattServices(bluetoothService?.getSupportedGattServices())
                }
            }
        }
    }
}

class DeviceControlsActivity extends AppCompatActivity {

...

    private final BroadcastReceiver gattUpdateReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            final String action = intent.getAction();
            if (BluetoothLeService.ACTION_GATT_CONNECTED.equals(action)) {
                connected = true;
                updateConnectionState(R.string.connected);
            } else if (BluetoothLeService.ACTION_GATT_DISCONNECTED.equals(action)) {
                connected = false;
                updateConnectionState(R.string.disconnected);
            } else if (BluetoothLeService.ACTION_GATT_SERVICES_DISCOVERED.equals(action)) {
                // Show all the supported services and characteristics on the user interface.
                displayGattServices(bluetoothService.getSupportedGattServices());
            }
        }
    };
}

قراءة خصائص تقنية BLE

وعندما يتصل تطبيقك بخادم GATT ويكتشف الخدمات، يمكنه قراءة السمات وكتابتها، إذا كان ذلك متاحًا. على سبيل المثال، يتكرر المقتطف التالي بين خدمات الخادم وخصائصه ويعرضها في واجهة المستخدم:

class DeviceControlActivity : Activity() {

    // Demonstrates how to iterate through the supported GATT
    // Services/Characteristics.
    // In this sample, we populate the data structure that is bound to the
    // ExpandableListView on the UI.
    private fun displayGattServices(gattServices: List<BluetoothGattService>?) {
        if (gattServices == null) return
        var uuid: String?
        val unknownServiceString: String = resources.getString(R.string.unknown_service)
        val unknownCharaString: String = resources.getString(R.string.unknown_characteristic)
        val gattServiceData: MutableList<HashMap<String, String>> = mutableListOf()
        val gattCharacteristicData: MutableList<ArrayList<HashMap<String, String>>> =
                mutableListOf()
        mGattCharacteristics = mutableListOf()

        // Loops through available GATT Services.
        gattServices.forEach { gattService ->
            val currentServiceData = HashMap<String, String>()
            uuid = gattService.uuid.toString()
            currentServiceData[LIST_NAME] = SampleGattAttributes.lookup(uuid, unknownServiceString)
            currentServiceData[LIST_UUID] = uuid
            gattServiceData += currentServiceData

            val gattCharacteristicGroupData: ArrayList<HashMap<String, String>> = arrayListOf()
            val gattCharacteristics = gattService.characteristics
            val charas: MutableList<BluetoothGattCharacteristic> = mutableListOf()

            // Loops through available Characteristics.
            gattCharacteristics.forEach { gattCharacteristic ->
                charas += gattCharacteristic
                val currentCharaData: HashMap<String, String> = hashMapOf()
                uuid = gattCharacteristic.uuid.toString()
                currentCharaData[LIST_NAME] = SampleGattAttributes.lookup(uuid, unknownCharaString)
                currentCharaData[LIST_UUID] = uuid
                gattCharacteristicGroupData += currentCharaData
            }
            mGattCharacteristics += charas
            gattCharacteristicData += gattCharacteristicGroupData
        }
    }
}

public class DeviceControlActivity extends Activity {
    ...
    // Demonstrates how to iterate through the supported GATT
    // Services/Characteristics.
    // In this sample, we populate the data structure that is bound to the
    // ExpandableListView on the UI.
    private void displayGattServices(List<BluetoothGattService> gattServices) {
        if (gattServices == null) return;
        String uuid = null;
        String unknownServiceString = getResources().
                getString(R.string.unknown_service);
        String unknownCharaString = getResources().
                getString(R.string.unknown_characteristic);
        ArrayList<HashMap<String, String>> gattServiceData =
                new ArrayList<HashMap<String, String>>();
        ArrayList<ArrayList<HashMap<String, String>>> gattCharacteristicData
                = new ArrayList<ArrayList<HashMap<String, String>>>();
        mGattCharacteristics =
                new ArrayList<ArrayList<BluetoothGattCharacteristic>>();

        // Loops through available GATT Services.
        for (BluetoothGattService gattService : gattServices) {
            HashMap<String, String> currentServiceData =
                    new HashMap<String, String>();
            uuid = gattService.getUuid().toString();
            currentServiceData.put(
                    LIST_NAME, SampleGattAttributes.
                            lookup(uuid, unknownServiceString));
            currentServiceData.put(LIST_UUID, uuid);
            gattServiceData.add(currentServiceData);

            ArrayList<HashMap<String, String>> gattCharacteristicGroupData =
                    new ArrayList<HashMap<String, String>>();
            List<BluetoothGattCharacteristic> gattCharacteristics =
                    gattService.getCharacteristics();
            ArrayList<BluetoothGattCharacteristic> charas =
                    new ArrayList<BluetoothGattCharacteristic>();
           // Loops through available Characteristics.
            for (BluetoothGattCharacteristic gattCharacteristic :
                    gattCharacteristics) {
                charas.add(gattCharacteristic);
                HashMap<String, String> currentCharaData =
                        new HashMap<String, String>();
                uuid = gattCharacteristic.getUuid().toString();
                currentCharaData.put(
                        LIST_NAME, SampleGattAttributes.lookup(uuid,
                                unknownCharaString));
                currentCharaData.put(LIST_UUID, uuid);
                gattCharacteristicGroupData.add(currentCharaData);
            }
            mGattCharacteristics.add(charas);
            gattCharacteristicData.add(gattCharacteristicGroupData);
         }
    ...
    }
...
}

توفر خدمة GATT قائمة بالخصائص التي يمكنك قراءتها من الجهاز. للاستعلام عن البيانات، استدعِ الدالة readCharacteristic() في BluetoothGatt، مع تمرير BluetoothGattCharacteristic التي تريد قراءتها.

class BluetoothLeService : Service() {

...

    fun readCharacteristic(characteristic: BluetoothGattCharacteristic) {
        bluetoothGatt?.let { gatt ->
            gatt.readCharacteristic(characteristic)
        } ?: run {
            Log.w(TAG, "BluetoothGatt not initialized")
            Return
        }
    }
}

class BluetoothService extends Service {

...

    public void readCharacteristic(BluetoothGattCharacteristic characteristic) {
        if (bluetoothGatt == null) {
            Log.w(TAG, "BluetoothGatt not initialized");
            return;
        }
        bluetoothGatt.readCharacteristic(characteristic);
    }
}

في هذا المثال، تنفِّذ الخدمة دالة لاستدعاء readCharacteristic(). هذه مكالمة غير متزامنة. يتم إرسال النتائج إلى دالة BluetoothGattCallback onCharacteristicRead().

class BluetoothLeService : Service() {

...

    private val bluetoothGattCallback = object : BluetoothGattCallback() {

        ...

        override fun onCharacteristicRead(
            gatt: BluetoothGatt,
            characteristic: BluetoothGattCharacteristic,
            status: Int
            ) {
                if (status == BluetoothGatt.GATT_SUCCESS) {
                broadcastUpdate(BluetoothService.ACTION_DATA_AVAILABLE, characteristic)
            }
        }
    }
}

class BluetoothService extends Service {

...

    private final BluetoothGattCallback bluetoothGattCallback = new BluetoothGattCallback() {

    ...

        @Override
        public void onCharacteristicRead(
        BluetoothGatt gatt,
        BluetoothGattCharacteristic characteristic,
        int status
        ) {
            if (status == BluetoothGatt.GATT_SUCCESS) {
                broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
            }
        }
    };
}

عند تشغيل معاودة اتصال معيّنة، يتم استدعاء طريقة مساعد broadcastUpdate() المناسبة وتوجيهها لإجراء. تجدُر الإشارة إلى أنّه يتم تحليل البيانات في هذا القسم وفقًا لمواصفات الملف الشخصي لقياس معدّل نبضات القلب عن طريق البلوتوث.

private fun broadcastUpdate(action: String, characteristic: BluetoothGattCharacteristic) {
    val intent = Intent(action)

    // This is special handling for the Heart Rate Measurement profile. Data
    // parsing is carried out as per profile specifications.
    when (characteristic.uuid) {
        UUID_HEART_RATE_MEASUREMENT -> {
            val flag = characteristic.properties
            val format = when (flag and 0x01) {
                0x01 -> {
                    Log.d(TAG, "Heart rate format UINT16.")
                    BluetoothGattCharacteristic.FORMAT_UINT16
                }
                else -> {
                    Log.d(TAG, "Heart rate format UINT8.")
                    BluetoothGattCharacteristic.FORMAT_UINT8
                }
            }
            val heartRate = characteristic.getIntValue(format, 1)
            Log.d(TAG, String.format("Received heart rate: %d", heartRate))
            intent.putExtra(EXTRA_DATA, (heartRate).toString())
        }
        else -> {
            // For all other profiles, writes the data formatted in HEX.
            val data: ByteArray? = characteristic.value
            if (data?.isNotEmpty() == true) {
                val hexString: String = data.joinToString(separator = " ") {
                    String.format("%02X", it)
                }
                intent.putExtra(EXTRA_DATA, "$data\n$hexString")
            }
        }
    }
    sendBroadcast(intent)
}

private void broadcastUpdate(final String action,
                             final BluetoothGattCharacteristic characteristic) {
    final Intent intent = new Intent(action);

    // This is special handling for the Heart Rate Measurement profile. Data
    // parsing is carried out as per profile specifications.
    if (UUID_HEART_RATE_MEASUREMENT.equals(characteristic.getUuid())) {
        int flag = characteristic.getProperties();
        int format = -1;
        if ((flag & 0x01) != 0) {
            format = BluetoothGattCharacteristic.FORMAT_UINT16;
            Log.d(TAG, "Heart rate format UINT16.");
        } else {
            format = BluetoothGattCharacteristic.FORMAT_UINT8;
            Log.d(TAG, "Heart rate format UINT8.");
        }
        final int heartRate = characteristic.getIntValue(format, 1);
        Log.d(TAG, String.format("Received heart rate: %d", heartRate));
        intent.putExtra(EXTRA_DATA, String.valueOf(heartRate));
    } else {
        // For all other profiles, writes the data formatted in HEX.
        final byte[] data = characteristic.getValue();
        if (data != null && data.length > 0) {
            final StringBuilder stringBuilder = new StringBuilder(data.length);
            for(byte byteChar : data)
                stringBuilder.append(String.format("%02X ", byteChar));
            intent.putExtra(EXTRA_DATA, new String(data) + "\n" +
                    stringBuilder.toString());
        }
    }
    sendBroadcast(intent);
}

تلقّي إشعارات GATT

من الشائع أن تطلب تطبيقات BLE تلقّي إشعار عند تغيُّر خاصية معيَّنة على الجهاز. في المثال التالي، تنفِّذ الخدمة دالة لاستدعاء الطريقة setCharacteristicNotification():

class BluetoothLeService : Service() {

...

    fun setCharacteristicNotification(
    characteristic: BluetoothGattCharacteristic,
    enabled: Boolean
    ) {
        bluetoothGatt?.let { gatt ->
        gatt.setCharacteristicNotification(characteristic, enabled)

        // This is specific to Heart Rate Measurement.
        if (BluetoothService.UUID_HEART_RATE_MEASUREMENT == characteristic.uuid) {
            val descriptor = characteristic.getDescriptor(UUID.fromString(SampleGattAttributes.CLIENT_CHARACTERISTIC_CONFIG))
            descriptor.value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE
            gatt.writeDescriptor(descriptor)
        }
        } ?: run {
            Log.w(BluetoothService.TAG, "BluetoothGatt not initialized")
        }
    }
}

class BluetoothService extends Service {

...

    public void setCharacteristicNotification(BluetoothGattCharacteristic characteristic,boolean enabled) {
        if (bluetoothGatt == null) {
            Log.w(TAG, "BluetoothGatt not initialized");
            Return;
        }
        bluetoothGatt.setCharacteristicNotification(characteristic, enabled);

        // This is specific to Heart Rate Measurement.
        if (UUID_HEART_RATE_MEASUREMENT.equals(characteristic.getUuid())) {
            BluetoothGattDescriptor descriptor = characteristic.getDescriptor(UUID.fromString(SampleGattAttributes.CLIENT_CHARACTERISTIC_CONFIG));
            descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
            bluetoothGatt.writeDescriptor(descriptor);
        }
    }
}

بعد تفعيل الإشعارات لإحدى السمات، يتم تشغيل معاودة الاتصال بـ onCharacteristicChanged() في حال تغيّرت السمة على الجهاز البعيد:

class BluetoothLeService : Service() {

...

    private val bluetoothGattCallback = object : BluetoothGattCallback() {
        ...

        override fun onCharacteristicChanged(
        gatt: BluetoothGatt,
        characteristic: BluetoothGattCharacteristic
        ) {
            broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic)
        }
    }
}

class BluetoothService extends Service {

...

    private final BluetoothGattCallback bluetoothGattCallback = new BluetoothGattCallback() {
    ...

        @Override
        public void onCharacteristicChanged(
        BluetoothGatt gatt,
        BluetoothGattCharacteristic characteristic
        ) {
            broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
        }
    };
}