Multiple BluetoothGattCharacteristic not being notified

Question

I am working on a BLE device and am not able to get onCharacteristicChanged to ever be called. I have 8 BluetoothGattCharacteristic that I need to be subscribed to.

After I find the device onServicesDiscovered I start a process to subscribe to each characteristic.

private fun requestCharacteristics(gatt: BluetoothGatt, char: BluetoothGattCharacteristic){
        subscribeToCharacteristic(gatt, char, true)
        (charList).getOrNull(0)?.let {
            charList.removeAt(0)
        }
    }

Then in subscribeToCharacteristic I do all checking for the descriptor.

private val CHARACTERISTIC_UPDATE_NOTIFICATION_DESCRIPTOR_UUID = UUID.fromString("00002902-0000-1000-8000-00805f9b34fb")

private fun subscribeToCharacteristic(gatt: BluetoothGatt, char: BluetoothGattCharacteristic, enable: Boolean) {
        if (gatt.setCharacteristicNotification(char, enable)){
            val descriptor = char.getDescriptor(CHARACTERISTIC_UPDATE_NOTIFICATION_DESCRIPTOR_UUID)
            if (descriptor != null){
                if (BluetoothGattCharacteristic.PROPERTY_NOTIFY != 0 && char.properties != 0) {
                    descriptor.value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE
                } else if (BluetoothGattCharacteristic.PROPERTY_INDICATE != 0 && char.properties != 0) {
                    descriptor.value = BluetoothGattDescriptor.ENABLE_INDICATION_VALUE
                } else {
                    println("The characteristic does not have NOTIFY or INDICATE property set")

                }
                if (gatt.writeDescriptor(descriptor)){
                    println("this worked")
                } else {
                    println("This did not work")
                }
            } else {
                println("Failed to set client characteristic notification")
            }
        } else {
            println("Failed to register notification")
        }

    }

I then get a call for each characteristic in onDescriptorWrite and check if I need to subscribe to another characteristic.

override fun onDescriptorWrite(gatt: BluetoothGatt, descriptor: BluetoothGattDescriptor?, status: Int) {
        super.onDescriptorWrite(gatt, descriptor, status)
        if (signalsChars.isNotEmpty()) {
            requestCharacteristics(gatt, signalsChars.first())
        } 
    }

All of this works but I never get any calls from onCharacteristicChanged. Also, if I call gatt.readCharacteristic(char) before I subscribe, onDescriptorWrite will not be called. Again I have 8 characteristics I need to subscribe to. Please help!

score 0 · Answer 1 · answered Sep 02 '18 at 17:41

I've made a simple BLE Client Android app in Kotlin recently. You can find its code here. Maybe it will help you.

After I've subscribed with gatt.setCharacteristicNotification I got notified every time the characteristic changed, so I think you got it right. Are you sure that the characteristic on BLE device changes?

Also if you have a situation where you read characteristic before subscribing to it, you can use onCharacteristicRead method. It get's called when the characteristic is read, so you can get the descriptor and write to it there.

Multiple BluetoothGattCharacteristic not being notified

1 Answers1