Subscribe to a BLE Gatt notification Android

Question

I´m developing an BLE app, based on the Gatt sample project provided by google: https://developer.android.com/samples/BluetoothLeGatt/index.html. So, I can send data writing in a characteristic successfully. Now I need to know when this characteristic change its value. I understand that I need to implement the setCharacteristicNotification() method and the onDescriptorWrite() method. But I cant do that this works. Searching, I found some ideas about that: Android BLE API: GATT Notification not received, What are the steps to get notified by Bluetooth Low Energy (BLE) device?, but still no luck I dont understand how it works, what parameter I need define or what I need to do!!!. Some good soul can share me a complete project that do this. All that I need is visualize the value of the characteristic when the BLE device returns some data.

I read the official Android documentation, but it is not so specific about that. Thanks in advance

These are my codes:

Device

public class DeviceControlActivity extends Activity {  public static final String EXTRAS_DEVICE_NAME = "DEVICE_NAME"; public static final String EXTRAS_DEVICE_ADDRESS = "DEVICE_ADDRESS";  private TextView mConnectionState; private TextView mDataField; private TextView mRssiField; private String mDeviceName; private String mDeviceAddress; private ExpandableListView mGattServicesList; private BluetoothLeService mBluetoothLeService; static ArrayList<ArrayList<BluetoothGattCharacteristic>> mGattCharacteristics = new      ArrayList<ArrayList<BluetoothGattCharacteristic>>(); private boolean mConnected = false; private BluetoothGattCharacteristic mNotifyCharacteristic; private BluetoothGattCharacteristic mWriteCharacteristic, mReadCharacteristic; Button Escritor; byte hello[] = { 0 };  private final String LIST_NAME = "NAME"; private final String LIST_UUID = "UUID";  //  BluetoothGattCharacteristic characteristic;  //  public BluetoothGatt mBluetoothGatt; // Code to manage Service lifecycle. private final ServiceConnection mServiceConnection = new ServiceConnection() {      @Override     public void onServiceConnected(ComponentName componentName, IBinder service) {         mBluetoothLeService = ((BluetoothLeService.LocalBinder) service).getService();         if (!mBluetoothLeService.initialize()) {             Log.e("Unable to initialize Bluetooth");             finish();         }         // Automatically connects to the device upon successful start-up         // initialization.         mBluetoothLeService.connect(mDeviceAddress);         mBluetoothLeService.setBLEServiceCb(mDCServiceCb);     }      @Override     public void onServiceDisconnected(ComponentName componentName) {         mBluetoothLeService = null;     } };  // If a given GATT characteristic is selected, check for supported features. // This sample // demonstrates 'Read' and 'Notify' features. See // http://d.android.com/reference/android/bluetooth/BluetoothGatt.html for // the complete // list of supported characteristic features. private final ExpandableListView.OnChildClickListener servicesListClickListner = new ExpandableListView.OnChildClickListener() {     @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)     @Override     public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {         if (mGattCharacteristics != null) {             final BluetoothGattCharacteristic characteristic = mGattCharacteristics.get(groupPosition).get(childPosition);             final int charaProp = characteristic.getProperties();             if ((charaProp & BluetoothGattCharacteristic.PROPERTY_READ) > 0) {                 // If there is an active notification on a characteristic,                 // clear                 // it first so it doesn't update the data field on the user                 // interface.                 Log.d("BluetoothGattCharacteristic has PROPERTY_READ, so send read request");                  if (mNotifyCharacteristic != null) {                     mBluetoothLeService.setCharacteristicNotification(mNotifyCharacteristic, true);                     mNotifyCharacteristic = null;                 }                 mBluetoothLeService.readCharacteristic(characteristic);                 /*Toast.makeText(getApplicationContext(), "Leyó Algo",                         Toast.LENGTH_SHORT).show();*/             }              if ((charaProp & BluetoothGattCharacteristic.PROPERTY_NOTIFY) > 0) {                 Log.d("BluetoothGattCharacteristic has PROPERTY_NOTIFY, so send notify request");                  mNotifyCharacteristic = characteristic;                 mBluetoothLeService.setCharacteristicNotification(characteristic, true);             }              if (((charaProp & BluetoothGattCharacteristic.PROPERTY_WRITE) | (charaProp & BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE)) > 0) {                 Log.d("BluetoothGattCharacteristic has PROPERY_WRITE | PROPERTY_WRITE_NO_RESPONSE");                  mWriteCharacteristic = characteristic;                 // popup an dialog to write something.                 showCharactWriteDialog();             }             return true;         }         return false;     } };  private void showCharactWriteDialog() {     DialogFragment newFrame = new BleCharacterDialogFragment();     newFrame.show(getFragmentManager(), "blewrite"); }  private void clearUI() {     mGattServicesList.setAdapter((SimpleExpandableListAdapter) null);     mDataField.setText(R.string.no_data); }  @TargetApi(Build.VERSION_CODES.HONEYCOMB) @Override public void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     setContentView(R.layout.gatt_services_characteristics);      final Intent intent = getIntent();     mDeviceName = intent.getStringExtra(EXTRAS_DEVICE_NAME);     mDeviceAddress = intent.getStringExtra(EXTRAS_DEVICE_ADDRESS);      // Sets up UI references.     ((TextView) findViewById(R.id.device_address)).setText(mDeviceAddress);     mGattServicesList = (ExpandableListView) findViewById(R.id.gatt_services_list);     mGattServicesList.setOnChildClickListener(servicesListClickListner);     mConnectionState = (TextView) findViewById(R.id.connection_state);     mDataField = (TextView) findViewById(R.id.data_value);     mRssiField = (TextView) findViewById(R.id.signal_rssi);      getActionBar().setTitle(mDeviceName);     getActionBar().setDisplayHomeAsUpEnabled(true);     Intent gattServiceIntent = new Intent(this, BluetoothLeService.class);     bindService(gattServiceIntent, mServiceConnection, BIND_AUTO_CREATE); }  @Override protected void onResume() {     super.onResume();     // registerReceiver(mGattUpdateReceiver, makeGattUpdateIntentFilter());     if (mBluetoothLeService != null) {         final boolean result = mBluetoothLeService.connect(mDeviceAddress);         Log.d("Connect request result=" + result);     } }  @Override protected void onPause() {     super.onPause();     // unregisterReceiver(mGattUpdateReceiver); }  @Override protected void onDestroy() {     super.onDestroy();     unbindService(mServiceConnection);     mBluetoothLeService = null; }  @Override public boolean onCreateOptionsMenu(Menu menu) {     getMenuInflater().inflate(R.menu.gatt_services, menu);     if (mConnected) {         menu.findItem(R.id.menu_connect).setVisible(false);         menu.findItem(R.id.menu_disconnect).setVisible(true);     } else {         menu.findItem(R.id.menu_connect).setVisible(true);         menu.findItem(R.id.menu_disconnect).setVisible(false);     }     return true; }  @TargetApi(Build.VERSION_CODES.ECLAIR) @Override public boolean onOptionsItemSelected(MenuItem item) {     switch (item.getItemId()) {     case R.id.menu_connect:         mBluetoothLeService.connect(mDeviceAddress);         return true;     case R.id.menu_disconnect:         mBluetoothLeService.disconnect();         return true;     case android.R.id.home:         onBackPressed();         return true;     }     return super.onOptionsItemSelected(item); }  private void updateConnectionState(final int resourceId) {     runOnUiThread(new Runnable() {         @Override         public void run() {             mConnectionState.setText(resourceId);         }     }); }  private void displayData(String data) {     if (data != null) {         mDataField.setText(data);      } }  private void displayRssi(String rssi) {     if (rssi != null) {         // Log.d("-- dispaly Rssi: " + rssi);         mRssiField.setText(rssi);     } }  private void displayRetorno(String rssi) {      if (rssi != null) {         // Log.d("-- dispaly Rssi: " + rssi);         mRssiField.setText(rssi+"Ñ");         Toast.makeText(getApplicationContext(), "SsSsSs"+"viendo", Toast.LENGTH_SHORT).show();     } }  // 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. @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2) private void displayGattServices(List<BluetoothGattService> gattServices) {     Log.d("displayGATTServices");      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);     }      SimpleExpandableListAdapter gattServiceAdapter = new SimpleExpandableListAdapter(this, gattServiceData, android.R.layout.simple_expandable_list_item_2, new String[] { LIST_NAME, LIST_UUID },             new int[] { android.R.id.text1, android.R.id.text2 }, gattCharacteristicData, android.R.layout.simple_expandable_list_item_2, new String[] { LIST_NAME, LIST_UUID }, new int[] {                     android.R.id.text1, android.R.id.text2 });     mGattServicesList.setAdapter(gattServiceAdapter);       final BluetoothGattCharacteristic characteristic = mGattCharacteristics.get(2).get(0);     final int charaProp = characteristic.getProperties();     mWriteCharacteristic = characteristic;     mBluetoothLeService.setCharacteristicNotification(mWriteCharacteristic, true);      if (mWriteCharacteristic != null) {         byte[] value = { (byte) 0x0D };         mWriteCharacteristic.setValue("ATZ");         Toast.makeText(getApplicationContext(), String.valueOf(mWriteCharacteristic.getStringValue(0)), Toast.LENGTH_SHORT).show();         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue(value);         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         boolean jo=mBluetoothLeService.mBluetoothGatt.readCharacteristic(mWriteCharacteristic);         Toast.makeText(getApplicationContext(), String.valueOf(mWriteCharacteristic.getStringValue(0)), Toast.LENGTH_SHORT).show();          /*mWriteCharacteristic.setValue("ATE0");         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue(value);         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue("ATE0");         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue(value);         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue("ATL0");         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue(value);         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue("ATM0");         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue(value);         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue("ATS0");         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue(value);         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue("ATH0");         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue(value);         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue("ATAT2");         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue(value);         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);*/         /*mWriteCharacteristic.setValue("ATZ");         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);         mWriteCharacteristic.setValue(value);         mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);*/      }      final BluetoothGattCharacteristic characteristic2 = mGattCharacteristics.get(0).get(0);     final int charaProp2 = characteristic2.getProperties();      mReadCharacteristic = characteristic2;     mBluetoothLeService.readCharacteristic(mReadCharacteristic); }    private DCServiceCb mDCServiceCb = new DCServiceCb();  public class DCServiceCb implements BluetoothLeService.BLEServiceCallback {      @Override     public void displayRssi(final int rssi) {         runOnUiThread(new Runnable() {             @Override             public void run() {                  DeviceControlActivity.this.displayRssi(String.valueOf(rssi));             }         });     }      @Override     public void displayRetorno (final int rssi) {         runOnUiThread(new Runnable() {             @Override             public void run() {                  DeviceControlActivity.this.displayRetorno("algo!!!!");             }         });     }      @Override     public void displayData(final String data) {         runOnUiThread(new Runnable() {             @Override             public void run() {                 DeviceControlActivity.this.displayData(data);                 Toast.makeText(getApplicationContext(), data+"SsSsSs", Toast.LENGTH_SHORT).show();             }         });     }      @Override     public void notifyConnectedGATT() {         runOnUiThread(new Runnable() {             @Override             public void run() {                 mConnected = true;                 updateConnectionState(R.string.connected);                 invalidateOptionsMenu();             }         });     }      @Override     public void notifyDisconnectedGATT() {         runOnUiThread(new Runnable() {             @Override             public void run() {                 mConnected = false;                 updateConnectionState(R.string.disconnected);                 invalidateOptionsMenu();                 clearUI();             }         });     }      @Override     public void displayGATTServices() {         Log.d("displayGATTServices.");         runOnUiThread(new Runnable() {             @Override             public void run() {                 if (mBluetoothLeService != null) {                     DeviceControlActivity.this.displayGattServices(mBluetoothLeService.getSupportedGattServices());                 }             }         });     } }  @SuppressLint("ValidFragment") public class BleCharacterDialogFragment extends DialogFragment {      @Override     public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {         View v = inflater.inflate(R.layout.write_charact_dialog, container, false);         final EditText ed = (EditText) v.findViewById(R.id.charact_value);         Button ok = (Button) v.findViewById(R.id.dialog_confirm);         Button cancel = (Button) v.findViewById(R.id.dialog_cancel);          ok.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                   if (mWriteCharacteristic != null) {                     mWriteCharacteristic.setValue("AA");                     mBluetoothLeService.mBluetoothGatt.writeCharacteristic(mWriteCharacteristic);                 }                  // characteristic.setValue("FF");                 // characteristic.setValue(new byte[] {(byte) 0xFF});                 // writeCharacteristicValue(characteristic);                 //                 Toast.makeText(getApplicationContext(), "Se envío el dato", Toast.LENGTH_SHORT).show();                 dismiss();                 return;             }         });          cancel.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 dismiss();             }         });          return v;     } }  public void writeCharacteristicValue(BluetoothGattCharacteristic characteristica) {     byte[] value = { (byte) 0xFF };     characteristica.setValue(bytesToHex(value));     boolean status = mBluetoothLeService.mBluetoothGatt.writeCharacteristic(characteristica); }  final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();  public String bytesToHex(byte[] bytes) {     char[] hexChars = new char[bytes.length * 2];     int v;     for (int j = 0; j < bytes.length; j++) {         v = bytes[j] & 0xFF;         hexChars[j * 2] = hexArray[v >>> 4];         hexChars[j * 2 + 1] = hexArray[v & 0x0F];     }     return new String(hexChars);  } } 

Service

@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2) public class BluetoothLeService extends Service { // private final static String TAG = // BluetoothLeService.class.getSimpleName();  private BluetoothManager mBluetoothManager; private BluetoothAdapter mBluetoothAdapter; private String mBluetoothDeviceAddress; BluetoothGatt mBluetoothGatt; private int mConnectionState = STATE_DISCONNECTED; private BLEServiceCallback mBLEServiceCb = null;  private static final int STATE_DISCONNECTED = 0; private static final int STATE_CONNECTING = 1; private static final int STATE_CONNECTED = 2; private static final int GATT_SUCCESS=0;  public final static UUID UUID_HEART_RATE_MEASUREMENT =  UUID.fromString(SampleGattAttributes.HEART_RATE_MEASUREMENT);  private final long READING_RSSI_TASK_FREQENCY = 500;  private static final int READ_RSSI_REPEAT = 1;  private final Handler mHandler = new Handler() {     @Override     public void handleMessage(Message msg) {         switch (msg.what) {         case READ_RSSI_REPEAT:             if (mBluetoothGatt != null) {                 mBluetoothGatt.readRemoteRssi();                 if(DeviceControlActivity.mGattCharacteristics.size()==3)                 {                     boolean pp=mBluetoothGatt.readCharacteristic(DeviceControlActivity.mGattCharacteristics.get(2).get(0));//                     //BluetoothGattCallback.onCharacteristicRead(mBluetoothGatt, DeviceControlActivity.mGattCharacteristics.get(2).get(0), GATT_SUCCESS);                 }             }             sendMessageDelayed(obtainMessage(READ_RSSI_REPEAT), READING_RSSI_TASK_FREQENCY);             break;         }     } };  private void startReadRssi() {     if (mHandler.hasMessages(READ_RSSI_REPEAT)) {         Log.w("+++++++++ Handler already has Message: READ_RSSI_REPEAT");     }     mHandler.sendEmptyMessage(READ_RSSI_REPEAT); }  private void stopReadRssi() {     mHandler.removeMessages(READ_RSSI_REPEAT); }  // Implements callback methods for GATT events that the app cares about. For // example, // connection change and services discovered. private final BluetoothGattCallback mGattCallback = new BluetoothGattCallback() {     @Override     public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {         Log.d("onConnectionStateChange status = " + status + ", newState = " + newState);          if (newState == BluetoothProfile.STATE_CONNECTED) {             if (mBLEServiceCb != null) {                 mBLEServiceCb.notifyConnectedGATT();             }              Log.d("Connected to GATT server.");             // Attempts to discover services after successful connection.             Log.d("Attempting to start service discovery:" + mBluetoothGatt.discoverServices());             startReadRssi();             //si se conecta empiece a leer mi caracteritica          } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {             if (mBLEServiceCb != null) {                 mBLEServiceCb.notifyDisconnectedGATT();             }             stopReadRssi();             Log.d("Disconnected from GATT server.");         }     }      @Override     public void onServicesDiscovered(BluetoothGatt gatt, int status) {         Log.d("onServicesDiscovered status = " + status);          if (status == BluetoothGatt.GATT_SUCCESS) {             if (mBLEServiceCb != null) {                 mBLEServiceCb.displayGATTServices();             }          } else {             Log.d("onServicesDiscovered received: " + status);         }         setCharacteristicNotification(DeviceControlActivity.mGattCharacteristics.get(2).get(0), true);//puede que sea mejor no ponerlo, pero no se     }      @Override     public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {         Log.d("onCharacteristicRead status: " + status);         Toast.makeText(getApplicationContext(), "MMMM"+"BBB"+"SsSsSs", Toast.LENGTH_SHORT).show();         if (status == BluetoothGatt.GATT_SUCCESS) {             displayCharacteristic(characteristic);         }     }      @Override     public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {         Log.d("------------- onCharacteristicWrite status: " + status);          // handler callback of write characteristic.         // do somethings here.     }      @Override     public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) {         Log.d("onCharacteristicChanged");         Toast.makeText(getApplicationContext(), "se ejecutó el metodo de cambio en caracteristica", Toast.LENGTH_SHORT).show();         displayCharacteristic(characteristic);     }      @Override     public void onReadRemoteRssi(BluetoothGatt gatt, int rssi, int status) {         // Log.d("onReadRemoteRssi rssi = " + rssi + "; status = " +         // status);         if (mBLEServiceCb != null) {             mBLEServiceCb.displayRssi(rssi);         }     } };  public void setBLEServiceCb(BLEServiceCallback cb) {     if (cb != null) {         mBLEServiceCb = cb;     } }  private void displayCharacteristic(final BluetoothGattCharacteristic characteristic) {     String msg = null;     // This is special handling for the Heart Rate Measurement profile. Data     // parsing is     // carried out as per profile specifications:     // http://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.heart_rate_measurement.xml     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("Heart rate format UINT16.");         } else {             format = BluetoothGattCharacteristic.FORMAT_UINT8;             Log.d("Heart rate format UINT8.");         }         final int heartRate = characteristic.getIntValue(format, 1);         Log.d(String.format("Received heart rate: %d", heartRate));          msg = 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));              msg = new String(data) + "\n" + stringBuilder.toString();         }     }      if (mBLEServiceCb != null) {         mBLEServiceCb.displayData(msg);     }  }  public class LocalBinder extends Binder {     BluetoothLeService getService() {         return BluetoothLeService.this;     } }  @Override public IBinder onBind(Intent intent) {     return mBinder; }  @Override public boolean onUnbind(Intent intent) {     close();     return super.onUnbind(intent); }  private final IBinder mBinder = new LocalBinder();  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("Unable to initialize BluetoothManager.");             return false;         }     }      mBluetoothAdapter = mBluetoothManager.getAdapter();     if (mBluetoothAdapter == null) {         Log.e("Unable to obtain a BluetoothAdapter.");         return false;     }      return true; }  public boolean connect(final String address) {     if (mBluetoothAdapter == null || address == null) {         Log.w("BluetoothAdapter not initialized or unspecified address.");         return false;     }      // Previously connected device. Try to reconnect.     if (mBluetoothDeviceAddress != null && address.equals(mBluetoothDeviceAddress) && mBluetoothGatt != null) {         Log.d("Trying to use an existing mBluetoothGatt for connection.");         if (mBluetoothGatt.connect()) {             mConnectionState = STATE_CONNECTING;             return true;         } else {             return false;         }     }      final BluetoothDevice device = mBluetoothAdapter.getRemoteDevice(address);     if (device == null) {         Log.w("Device not found.  Unable to connect.");         return false;     }     // We want to directly connect to the device, so we are setting the     // autoConnect     // parameter to false.     mBluetoothGatt = device.connectGatt(this, false, mGattCallback);     Log.d("Trying to create a new connection.");     mBluetoothDeviceAddress = address;     mConnectionState = STATE_CONNECTING;     return true; }  public void disconnect() {     if (mBluetoothAdapter == null || mBluetoothGatt == null) {         Log.w("BluetoothAdapter not initialized");         return;     }     mBluetoothGatt.disconnect(); }  public void close() {     if (mBluetoothGatt == null) {         return;     }     mBluetoothGatt.close();     mBluetoothGatt = null; }  /**  * Request a read on a given {@code BluetoothGattCharacteristic}. The read  * result is reported asynchronously through the  * {@code BluetoothGattCallback#onCharacteristicRead(android.bluetooth.BluetoothGatt, android.bluetooth.BluetoothGattCharacteristic, int)}  * callback.  *   * @param characteristic  *            The characteristic to read from.  */ public void readCharacteristic(BluetoothGattCharacteristic characteristic) {     Toast.makeText(getApplicationContext(), "readCharacteristic en Servicio", Toast.LENGTH_SHORT).show();     if (mBluetoothAdapter == null || mBluetoothGatt == null) {         Log.w("BluetoothAdapter not initialized");          return;     }     mBluetoothGatt.readCharacteristic(characteristic); }  /**  * Requst a write on a give {@code BluetoothGattCharacteristic}. The write  * result is reported asynchronously through the  * {@code BluetoothGattCallback#onCharacteristicWrite(andorid.bluetooth.BluetoothGatt, android.bluetooth.BluetoothGattCharacteristic, int)}  * callback.  */ public void writeCharacteristic(BluetoothGattCharacteristic characteristic) {     if (mBluetoothAdapter == null || mBluetoothGatt == null) {         Log.w("BluetoothAdapter not initialized");         return;     }     mBluetoothGatt.writeCharacteristic(characteristic); }  /**  * Enables or disables notification on a give characteristic.  *   * @param characteristic  *            Characteristic to act on.  * @param enabled  *            If true, enable notification. False otherwise.  */ public void setCharacteristicNotification(BluetoothGattCharacteristic characteristic, boolean enabled) {     if (mBluetoothAdapter == null || mBluetoothGatt == null) {         Log.w("BluetoothAdapter not initialized");         return;     }     mBluetoothGatt.setCharacteristicNotification(characteristic, true);      // 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);         mBluetoothGatt.writeDescriptor(descriptor);     } }  /**  * Retrieves a list of supported GATT services on the connected device. This  * should be invoked only after {@code BluetoothGatt#discoverServices()}  * completes successfully.  *   * @return A {@code List} of supported services.  */ public List<BluetoothGattService> getSupportedGattServices() {     if (mBluetoothGatt == null)         return null;      return mBluetoothGatt.getServices(); }  public interface BLEServiceCallback {     public void displayRssi(int rssi);      public void displayData(String data);      public void notifyConnectedGATT();      public void notifyDisconnectedGATT();      public void displayGATTServices();      public void displayRetorno(int rssi);  } } 

Answer 1

To receive notification in Android you need to set characteristic notification to true

gatt.setCharacteristicNotification(characteristic, true); 

You also need to set the client characteristic configuration descriptor 0x2902

// 0x2902 org.bluetooth.descriptor.gatt.client_characteristic_configuration.xml UUID uuid = UUID.fromString("00002902-0000-1000-8000-00805f9b34fb"); BluetoothGattDescriptor descriptor = characteristic.getDescriptor(uuid); descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE); gatt.writeDescriptor(descriptor); 

A better API would be for setCharacteristicNotification to set the descriptor, but unfortunately it doesn't seem to work that way.

Answer 2

In addition to the accepted answer, I had to set the Characteristic to WRITE_TYPE_DEFAULT when subscribing to peripheral running on OS X.

characteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_DEFAULT);