Kotlin Bluetooth Connection (KBC)

To create a Bluetooth connection with a printer in Kotlin, you can follow these steps:

1. Make sure your printer has Bluetooth capability and is enabled.
2. Also make sure that the device running your application has Bluetooth capability and is enabled.
3. Import the android.bluetooth package into your Kotlin project.
4. Create a BluetoothAdapter object to manage Bluetooth connections.

val bluetoothAdapter = BluetoothAdapter.getDefaultAdapter()

Check if Bluetooth is enabled on the device. If not, display a dialog asking the user for permission to enable it.

if (bluetoothAdapter == null || !bluetoothAdapter.isEnabled) {
    val enableBtIntent = Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE)
    startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT)
}

Search the list of available Bluetooth devices.

val pairedDevices: Set<BluetoothDevice> = bluetoothAdapter.bondedDevices

Select the printer device from the list of available Bluetooth devices and create an object  BluetoothDevice.

val printerDevice: BluetoothDevice? = pairedDevices.firstOrNull { device ->
    device.name == "NamaPrinterBluetooth"
}

Make sure to replace "BluetoothPrinterName" with the actual name of your Bluetooth printer.

Create a BluetoothSocket object to connect the device to the printer.

val printerSocket: BluetoothSocket? = printerDevice?.createRfcommSocketToServiceRecord(MY_UUID)

You must replace MY_UUID with the UUID provided by your Bluetooth printer manufacturer.

Finally, connect the socket to the printer and send the print data.

printerSocket?.connect()
val outputStream = printerSocket?.outputStream
outputStream?.write("Hello, world!".toByteArray())
printerSocket?.close()

Make sure to replace  "Hello, world!" with the actual data you want to print.

These are some steps you can follow to create a Bluetooth connection with a printer in Kotlin. However, keep in mind that the steps may vary slightly depending on the model and manufacturer of the Bluetooth printer you are using.

Project Example

SelectDeviceActivity.kt

package com.appsinthesky.bluetoothtutorial

import android.app.Activity
import android.bluetooth.BluetoothAdapter
import android.bluetooth.BluetoothDevice
import android.content.Intent
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.widget.AdapterView
import android.widget.ArrayAdapter
import kotlinx.android.synthetic.main.select_device_layout.*
import org.jetbrains.anko.toast

class SelectDeviceActivity : AppCompatActivity() {

    private var m_bluetoothAdapter: BluetoothAdapter? = null
    private lateinit var m_pairedDevices: Set<BluetoothDevice>
    private val REQUEST_ENABLE_BLUETOOTH = 1

    companion object {
        val EXTRA_ADDRESS: String = "Device_address"
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.select_device_layout)

        m_bluetoothAdapter = BluetoothAdapter.getDefaultAdapter()
        if(m_bluetoothAdapter == null) {
            toast("this device doesn't support bluetooth")
            return
        }
        if(!m_bluetoothAdapter!!.isEnabled) {
            val enableBluetoothIntent = Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE)
            startActivityForResult(enableBluetoothIntent, REQUEST_ENABLE_BLUETOOTH)
        }

        select_device_refresh.setOnClickListener{ pairedDeviceList() }

    }

    private fun pairedDeviceList() {
        m_pairedDevices = m_bluetoothAdapter!!.bondedDevices
        val list : ArrayList<BluetoothDevice> = ArrayList()

        if (!m_pairedDevices.isEmpty()) {
            for (device: BluetoothDevice in m_pairedDevices) {
                list.add(device)
                Log.i("device", ""+device)
            }
        } else {
            toast("no paired bluetooth devices found")
        }

        val adapter = ArrayAdapter(this, android.R.layout.simple_list_item_1, list)
        select_device_list.adapter = adapter
        select_device_list.onItemClickListener = AdapterView.OnItemClickListener { _, _, position, _ ->
            val device: BluetoothDevice = list[position]
            val address: String = device.address

            val intent = Intent(this, ControlActivity::class.java)
            intent.putExtra(EXTRA_ADDRESS, address)
            startActivity(intent)
        }
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if (requestCode == REQUEST_ENABLE_BLUETOOTH) {
            if (resultCode == Activity.RESULT_OK) {
                if (m_bluetoothAdapter!!.isEnabled) {
                    toast("Bluetooth has been enabled")
                } else {
                    toast("Bluetooth has been disabled")
                }
            } else if (resultCode == Activity.RESULT_CANCELED) {
                toast("Bluetooth enabling has been canceled")
            }
        }
    }
}

DeviceListActivity.java

package suman.com.andoirdbluetoothprint;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.Window;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.AdapterView.OnItemClickListener;

import java.util.Set;


public class DeviceListActivity extends Activity {
    protected static final String