Failed to read characteristic

[Octavelscx]

Hi there,

I'm pretty new with kotlin and bluetooth and I'm trying your nice library, scan device works perfectly, but when I want to connect to a device and read a characteristic I get a null return and this is what I get in log : (failed to read characteristic)

Here is my code :

 * Connect BLE device
 */
@SuppressLint("MissingPermission")
public fun connectBLE(ble:BLE, device: BLEDevice) {
    var name: String = device.name.toString()
    lifecycleScope.launch {
            ble.connect(device)?.let { connection ->
                // For watching bytes
                val value = connection.read("00002A29-0000-1000-8000-00805F9B34FB")
                Log.i("BLEDATA", "$value")

        }
}

I read that for reading 16 bits uuid with bluetooth low energy we have make uuid this form : 0000XXXX-0000-1000-8000–00805f9b34fb But maybe I'm wrong ?

I got the uuid 0x180A with nrf Connect App and this is marked Read and correspond to the manufacturer brand name string. I bet I'm doing something wrong but dont know what...

Thanks a lot !

[Octavelscx]

I think the issue comes from the BluetoothCharacteristic class

The method read uses gatt.readCharacteristic() of android library and this method is asynchronous :

https://developer.android.com/reference/android/bluetooth/BluetoothGatt

I tried with debugging and when I do breakpoints, it works and I get return value of the reading of characteristic. If I just run the app without breakpoint, it returns null value.

So I think it's about a delay of the read() method of the BluetoothCharacteristic.

But I'm too new in kotlin to provide you an correction but I hope someone will see this and help ! :) Thanks

[LeandroSQ]

Hello there 🙂 First of all, thank you for the interest. Awesome findings, these issues seem to be related to #13.

I will take a look on your suggestions as soon as possible, thanks.

[LeandroSQ]

FYI, your initial guess was spot on! I missed completely the async behavior for read();

Thank you :)

[LeandroSQ]

You can check out a fix for it on #23

[LeandroSQ]

Please try v1.8.0

[Octavelscx]

Thanks a lot man,

I'm testing v1.8.0 right now but I get no return after the onCharacteristicRead()

This is how I call it :

The execution never go in the if else statement...

With the debugger I can see that it get the characteristic value :

But the execution get stuck at this line :

As if it never returns to my method and therefore never fits in the if else statement above

Maybe I'm calling it wrong, but I tried the other method you give and I got the same issue For your information I attach this method to a button with a setOnClickListener like this :

Thanks for your help

[LeandroSQ]

Are you using observe too? In non-notifiable characteristics, the library fallback to a legacy observe, which uses read. Also one limitation as per today, is only one read per characteristic at-a-time.

So when you call read you should wait until it returns to call read for the same characteristic again. Other characteristics will work fine.

Are any of these edge scenarios affecting you?

[LeandroSQ]

Would you be so kind to provide a minimum reproducible sample project?

[Octavelscx]

My bad, it's perfectly working when I read notifiable characteristic, but when I want to read a non notifiable characteristic it's not working, don't really know why, but pretty sure it's on my side

Thanks again