What are the steps to get notified by Bluetooth Low Energy (BLE) device?

Question

I am working on a Bluetooth Low Energy (BLE) app. I have a BLE device (scale) which measures weight. I am able to connect with this device. But I am not getting how to read data

Answer 1

Refer the source code of sample application "bluetoothlegatt" provided on developer portal.

Sample service: http://developer.android.com/samples/BluetoothLeGatt/src/com.example.android.bluetoothlegatt/BluetoothLeService.html

Using service: http://developer.android.com/samples/BluetoothLeGatt/src/com.example.android.bluetoothlegatt/DeviceControlActivity.html

This example contains characteristics with read and notify properties. So you definitely find your solution. Please go to section with following code:(You may figure it out)

public void readCharacteristic(BluetoothGattCharacteristic characteristic) {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.readCharacteristic(characteristic);
    }

Answer 2

Had a device which required me to use

descriptor.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE)

instead of

descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE)

as explained in this question

Android BLE API: GATT Notification not received

Answer 3

you have to differentiate the value is notification or indication, and set respective value using descriptor.setValue. if you set wrongly, you will not get the value.

Answer 4

This one is working for me:

to notify master device that some characteristic is change, call this function on your pheripheral:

private BluetoothGattServer server;
//init....

//on BluetoothGattServerCallback...

//call this after change the characteristic
server.notifyCharacteristicChanged(device, characteristic, false);

in your master device: enable setCharacteristicNotification after discover the service:

@Override
    public void onServicesDiscovered(BluetoothGatt gatt, int status) {
        super.onServicesDiscovered(gatt, status);
        services = mGatt.getServices();
        for(BluetoothGattService service : services){
            if( service.getUuid().equals(SERVICE_UUID)) {
                characteristicData = service.getCharacteristic(CHAR_UUID);
                for (BluetoothGattDescriptor descriptor : characteristicData.getDescriptors()) {
                    descriptor.setValue( BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
                    mGatt.writeDescriptor(descriptor);
                }
                gatt.setCharacteristicNotification(characteristicData, true);
            }
        }
        if (dialog.isShowing()){
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    dialog.hide();
                }
            });
        }
   }

now you can check your characteristic value is change, for example onCharacteristicRead function :

@Override
public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
        Log.i("onCharacteristicRead", characteristic.toString());
        byte[] value=characteristic.getValue();
        String v = new String(value);
        Log.i("onCharacteristicRead", "Value: " + v);
}