bluetooth lowenergy - Any way to implement BLE notifications in Android-L preview

Question

This question is not about Android notificatinos, but BLE notifications (as the title may hint)

I have got basic BLE peripheral mode working on Android-L

Is there any way to implement BLE notifications in Android-L preview. I could do some thing like the following to make a charecteritic be able to notify, but trying to listen for

BluetoothGattCharacteristic firstServiceChar = new BluetoothGattCharacteristic(
        UUID.fromString(serviceOneCharUuid),
                BluetoothGattCharacteristic.PROPERTY_NOTIFY, BluetoothGattCharacteristic.PERMISSION_READ );

But in LightBlue app on iOS I cannot subscribe to this characteristic. Apprently there is no API that could be use to respond to the calls when a char is subscribed (like there are in iOS)

Kindly share your code if you have successfully enabled BLE notifications on Android-L

Answer 1

On top of what OP has done:

BluetoothGattCharacteristic firstServiceChar = new BluetoothGattCharacteristic(UUID.fromString(serviceOneCharUuid), BluetoothGattCharacteristic.PROPERTY_NOTIFY, BluetoothGattCharacteristic.PERMISSION_READ )

The next thing is to add a Client Characteristic Configuration descriptor (UUID is the 128 bit version of the 16 bit 0x2902 using the Bluetooth base UUID), so that the connected device can tell yours that it wants notifications (or indications), and then add that descriptor to your characteristic:

BluetoothGattDescriptor gD = new BluetoothGattDescriptor(UUID.fromString("00002902-0000-1000-8000-00805F9B34FB"), BluetoothGattDescriptor.PERMISSION_WRITE | BluetoothGattDescriptor.PERMISSION_READ);

firstServiceChar.addDescriptor(gD);

That UUID is from the Bluetooth spec. Apparently a device subscribes to notifications by updating this descriptor, so you've got to handle this in your BluetoothGattServerCallback by overriding onDescriptorWriteRequest:

@Override
public void onDescriptorWriteRequest (BluetoothDevice device, int requestId, BluetoothGattDescriptor descriptor, boolean preparedWrite, boolean responseNeeded, int offset, byte[] value) {

    btClient = device;  // perhaps add to some kind of collection of devices to update?

    // now tell the connected device that this was all successfull
    btGattServer.sendResponse(device, requestId, BluetoothGatt.GATT_SUCCESS, offset, value);

}

Now update your value and notify the connectee:

firstServiceChar.setValue("HI");
btGattServer.notifyCharacteristicChanged(btClient, firstServiceChar, false);

Hopefully this quick and dirty code will help, because it was OP's code that I used in the first place to even get basic peripheral mode working :)