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);
 }
}

Steinke

Did you check if GATT Server (BLE Device) has the notifications enabled, else notifications and indications won't work on GATT client (Android App in this case) – Cambridge

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.

Bighorn

I´m no so good android developer, then I copy and paste the part of code in several parts of my project (doing the respective adjust to my owns variables). Now I can reach the readCharacteristic() method, but now I have a question, how can a catch the value of the characteristic sending by my BLE device? if the onCharacteristicRead() not executed means that the code doesn't works? – Steinke

In order to read the characteristic, you need to do BluetoothGatt.readCharacteristic then in the BluetoothGattCallback.onCharacteristicChanged you're asynchronously notified when the value is read. – Bighorn

+1. Also it is equally necessary that the GATT Server (BLE Device) has the notifications enabled, else notifications and indications won't work on GATT client (Android App in this case) – Cambridge

Any idea why is does not seem to be possible to enable more than one notification ? Surely one should able able to enable notifications for multiple characteristics, – Koral

@DuncanGroenewald Android supports notifications on multiple characteristics. Check the properties on your characteristics to ensure that notifications are supported. – Bighorn

In case anyone else gets stuck on this - this is an asynchronous call, and once you've issued it you can't go off immediately sending bytes to the characteristic. You'll have to wait until onDescriptorWrite is fired inside your BluetoothGattCallback handler. – Laaspere

Actually it is possible to enable more than one notifications for multiple characteristics. The Android BLE API is made to receive a callback when you send a GATT command to the server or your BLE device before proceeding to the next command. So what you need to do is set a message handler in your Device control Activity that receives callbacks from the Service based on the corresponding GATT command – Vannesavanness

So If you want to read a value from your BLE device, you will have to wait for the corresponding GATT Callback before issuing the next GATT command. In the case of subscribing to a notification, you can issue the command after your message handler reveals the Callback for reading the value from your BLE device. – Vannesavanness

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);

Tyrelltyrian