BLE NOTIFY characteristic not notifying

Question

I need to communicate with a BLE thermometer. Workflow is:

1. Register notifications on NOTIFY characteristic
2. Write initialization string in WRITE, WRITE NO RESPONSE characteristic
3. Data starts coming in in registered NOTIFY characteristic

This process works perfectly from Nordic nRF Connect app.

However, when doing it myself using the following BluetoothGattCallback object, it fails - I never get updates - the onCharacteristicRead or onCharacteristicChanged callbacks never fire. Everything works, though - all methods that should return true on success do return true... Anyway, here is the BluetoothGattCallback:

private BluetoothGattCallback gattCallback = new BluetoothGattCallback() {
    /**
     * Callback indicating when GATT client has connected/disconnected to/from a remote
     * GATT server.
     *
     * @param gatt     GATT client
     * @param status   Status of the connect or disconnect operation.
     *                 {@link BluetoothGatt#GATT_SUCCESS} if the operation succeeds.
     * @param newState Returns the new connection state. Can be one of
     *                 {@link BluetoothProfile#STATE_DISCONNECTED} or
     *                 {@link BluetoothProfile#STATE_CONNECTED}
     */
    @Override
    public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
        if (newState == BluetoothGatt.STATE_CONNECTED) {
            gatt.discoverServices();
        } else {
            responseCharacteristic = null;
            isConnected = false;
            disconnected();
        }
    }

    /**
     * Callback invoked when the list of remote services, characteristics and descriptors
     * for the remote device have been updated, ie new services have been discovered.
     *
     * @param gatt   GATT client invoked {@link BluetoothGatt#discoverServices}
     * @param status {@link BluetoothGatt#GATT_SUCCESS} if the remote device
     */
    @Override
    public void onServicesDiscovered(BluetoothGatt gatt, int status) {
        Log.wtf("THERMO", "Services discovered");
        BluetoothGattService thermoService = gatt.getService(THERMO_SERVICE);
        if (thermoService != null) {
            Log.wtf("THERMO", "Have service");
            //Find the characteristic
            configChar = thermoService.getCharacteristic(THERMO_CONFIGURATION);
            responseCharacteristic = thermoService.getCharacteristic(THERMO_RESPONSE);
            if (responseCharacteristic != null)
                setCharacteristicNotification(responseCharacteristic, true);
            else
                incompatibleTarget();
        } else
            incompatibleTarget();
    }

    /**
     * Callback triggered as a result of a remote characteristic notification.
     *
     * @param gatt           GATT client the characteristic is associated with
     * @param characteristic Characteristic that has been updated as a result
     */
    @Override
    public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) {
        Log.wtf("THERMO", "onCharChanged");
        dataReceived(characteristic);
    }

    @Override
    public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
        Log.wtf("THERMO", "onCharRead");
        dataReceived(characteristic);
    }

    @Override
    public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
        Log.wtf("THERMO", "Write done");
        if (status == BluetoothGatt.GATT_SUCCESS) {
            Log.wtf("THERMO", "Write ok");
            if (responseCharacteristic != null) {
                Log.wtf("THERMO", "Have response");
                isConnected = true;
                connected();
            }
        } else {
        }
    }

    @Override
    public void onDescriptorWrite(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {
        Log.wtf("THERMO", "onDescWrite");
        if (status == BluetoothGatt.GATT_SUCCESS) {
            if (configChar != null) {
                Log.wtf("THERMO", "Have config");
                configChar.setValue(thermoConfigData);
                Log.wtf("THERMO", "Writing: " + gatt.writeCharacteristic(configChar));
            }
        }
    }
};

And here is the method for registering the notifications:

private void setCharacteristicNotification(BluetoothGattCharacteristic characteristic, boolean enabled) {
    gatt.setCharacteristicNotification(characteristic, enabled);
    BluetoothGattDescriptor descriptor = characteristic.getDescriptor(CLIENT_CHARACTERISTIC_CONFIG);
    if (descriptor != null) {
        if (enabled) {
            descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
        } else {
            descriptor.setValue(BluetoothGattDescriptor.DISABLE_NOTIFICATION_VALUE);
        }
        Log.wtf("THERMO", "notifyDesc: " + gatt.writeDescriptor(descriptor));
    }
}

The notification enabling method works with all other devices. Any ideas what I'm doing wrong?

Answer 1

For some reason, changing the callback code to this helped. Looks like you need to call getService and getCharacteristic in the callback you're using them, you can't keep them around in a variable...

private BluetoothGattCallback gattCallback = new BluetoothGattCallback() {
    /**
     * Callback indicating when GATT client has connected/disconnected to/from a remote
     * GATT server.
     *
     * @param gatt     GATT client
     * @param status   Status of the connect or disconnect operation.
     *                 {@link BluetoothGatt#GATT_SUCCESS} if the operation succeeds.
     * @param newState Returns the new connection state. Can be one of
     *                 {@link BluetoothProfile#STATE_DISCONNECTED} or
     *                 {@link BluetoothProfile#STATE_CONNECTED}
     */
    @Override
    public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
        if (newState == BluetoothGatt.STATE_CONNECTED) {
            gatt.discoverServices();
        } else {
            responseCharacteristic = null;
            isConnected = false;
            disconnected();
        }
    }

    /**
     * Callback invoked when the list of remote services, characteristics and descriptors
     * for the remote device have been updated, ie new services have been discovered.
     *
     * @param gatt   GATT client invoked {@link BluetoothGatt#discoverServices}
     * @param status {@link BluetoothGatt#GATT_SUCCESS} if the remote device
     */
    @Override
    public void onServicesDiscovered(BluetoothGatt gatt, int status) {
        Log.wtf("THERMO", "Services discovered");
        BluetoothGattService thermoService = gatt.getService(THERMO_SERVICE);
        if (thermoService != null) {
            Log.wtf("THERMO", "Have service");
            //Find the characteristic
            responseCharacteristic = thermoService.getCharacteristic(THERMO_RESPONSE);
            if (responseCharacteristic != null)
                setCharacteristicNotification(responseCharacteristic, true);
            else
                incompatibleTarget();
        } else
            incompatibleTarget();
    }

    /**
     * Callback triggered as a result of a remote characteristic notification.
     *
     * @param gatt           GATT client the characteristic is associated with
     * @param characteristic Characteristic that has been updated as a result
     */
    @Override
    public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) {
        Log.wtf("THERMO", "onCharChanged");
        dataReceived(characteristic);
    }

    @Override
    public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
        Log.wtf("THERMO", "onCharRead");
        dataReceived(characteristic);
    }

    @Override
    public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
        Log.wtf("THERMO", "Write done");
        if (status == BluetoothGatt.GATT_SUCCESS) {
            Log.wtf("THERMO", "Write ok");
            if (responseCharacteristic != null) {
                Log.wtf("THERMO", "Have response");
                isConnected = true;
                connected();
            }
        } else {
        }
    }

    @Override
    public void onDescriptorWrite(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {
        Log.wtf("THERMO", "onDescWrite");
        if (status == BluetoothGatt.GATT_SUCCESS) {
            BluetoothGattService thermoService = gatt.getService(THERMO_SERVICE);
            if (thermoService != null) {
                configChar = thermoService.getCharacteristic(THERMO_CONFIGURATION);
                if (configChar != null) {
                    Log.wtf("THERMO", "Have config");
                    configChar.setValue(thermoConfigData);
                    Log.wtf("THERMO", "Writing: " + gatt.writeCharacteristic(configChar));
                }
            }
        }
    }
};