Reflection and Invoking Method from Java to Kotlin

Question

I'm trying to convert the following reflection into Kotlin. The following uses reflection to call an RFCOMMs function so it can take a port/channel as an input instead of UUID. I have all my program in Kotlin. Anyone know how to write this in Kotlin?

int bt_port_to_connect = 5;
BluetoothDevice device = mDevice;
BluetoothSocket deviceSocket = null;
...

// IMPORTANT: we create a reference to the 'createInsecureRfcommSocket' method
// and not(!) to the 'createInsecureRfcommSocketToServiceRecord' (which is what the 
// android SDK documentation publishes

Method m = device.getClass().getMethod("createInsecureRfcommSocket", new Class[] {int.class});

deviceSocket = (BluetoothSocket) m.invoke(device,bt_port_to_connect);

Updating with recommendation:

class BluetoothClient(device: BluetoothDevice): Thread() {
    // https://stackoverflow.com/questions/9703779/connecting-to-a-specific-bluetooth-port-on-a-bluetooth-device-using-android
    // Need to reflection - create RFCOMM socket to a port number instead of UUID
    // Invoke btdevice as 1st parameter and then the port number

    var bt_port_to_connect = 5

    var deviceSocket: BluetoothSocket? = null


    private val socket = device.createInsecureRfcommSocketToServiceRecord(uuid)
    val m = device::class.declaredFunctions.single { it.name == "createInsecureRfcommSocket" }
    
    m.call(device, bt_port_to_connect)


    override fun run() {
        try {
            Log.i("client", "Connecting")
            this.socket.connect()

            Log.i("client", "Sending")
            val outputStream = this.socket.outputStream
            val inputStream = this.socket.inputStream
            try {
                outputStream.write(message.toByteArray())
                outputStream.flush()
                Log.i("client", "Sent")
            } catch(e: Exception) {
                Log.e("client", "Cannot send", e)
            } finally {
                outputStream.close()
                inputStream.close()
                this.socket.close()
            }
        }
        catch (e: IOException) {
            println("Socket Failed")
        }

    }
}

score 1 · Answer 1 · answered Jun 23 '21 at 20:20

1

You can really use exactly the same code, just convert it to Kotlin:

val m = device::class.java.getMethod("createInsecureRfcommSocket", Int::class.java)
m.invoke(device, bt_port_to_connect)

Or you can use Kotlin reflection:

val m = device::class.declaredFunctions.single { it.name == "createInsecureRfcommSocket" }
m.call(device, bt_port_to_connect)

I don't know if there is any better way to find a function with provided name. You can create an extension function to make it cleaner. You may also need to check parameters if this function has overrides.

answered Jun 23 '21 at 20:20

broot

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Thanks for the recommendation. I updated the code but now I'm getting a member declaration error with the "m.call(device, bt_port_to_connect)" line in both Java and Kotlin examples. Do you know why that is? – Stigma Jun 28 '21 at 19:24
You put this line of code directly into the body of a class. Class can't hold arbitrary code, but only definitions of properties, functions, etc. You need to put it into some function. When do you need to run this code? In a constructor? – broot Jun 28 '21 at 20:00
I am calling this class BluetoothClient(mmDevice).start() in a Composable Button onclick modifier hoping to start this bluetooth port connection. I updated the code above. Am I able to put the m.call into my BluetoothClient class's run() function? When I do this, the Run() function also cannot reference the bluetoothdevice parameter device from the class. – Stigma Jun 28 '21 at 20:07
If you need to put this code in `run()` then you need to also store `device` as an instance property like this: `class BluetoothClient(private val device: BluetoothDevice)`. – broot Jun 28 '21 at 20:11

Reflection and Invoking Method from Java to Kotlin

1 Answers1