Creating a simple foreground service

Contents
Define the constants needed
Create a service class
Define the channel creation
Define the runtime permission
Define the permissions in the manifest
Declare the service tag in the manifest
Initiate start and stop actions from your UI

Define the constants needed

object Constants {
    const val NOTIFICATION_CHANNEL_ID = "STOPWATCH_NOTIFICATION_ID"
    const val NOTIFICATION_CHANNEL_NAME = "STOPWATCH_NOTIFICATION"
    const val NOTIFICATION_ID = 10
}

Create a service class

class StopwatchService : Service() {

    override fun onBind(intent: Intent?): IBinder? {
        return null
    }

    /**
     * This method is triggered when another Android component sends the intent to the running service
     */
    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {

        when(intent?.action){
            Actions.START.toString() ->{
                start()
            }
            Actions.STOP.toString() ->{
                stopSelf()
            }
        }

        return super.onStartCommand(intent, flags, startId)
    }

    private fun start() {
        val notification = NotificationCompat
            .Builder(this,NOTIFICATION_CHANNEL_ID).setSmallIcon(R.mipmap.ic_launcher)
            .setContentTitle("Stop Watch")
            .setContentText("Content of the notification")
            .build()

        startForeground(NOTIFICATION_ID,notification)
    }


    enum class Actions{
        START, STOP
    }

}

Define the channel creation

MyApplication.kt

class MyApplication: Application() {
    override fun onCreate() {
        super.onCreate()
        if(Build.VERSION.SDK_INT >= (Build.VERSION_CODES.O)){
            val channel = NotificationChannel(
                NOTIFICATION_CHANNEL_ID,
                NOTIFICATION_CHANNEL_NAME ,
                NotificationManager.IMPORTANCE_HIGH
            )
            val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
            notificationManager.createNotificationChannel(channel)
        }
    }
}

Define the runtime permission

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        if (Build.VERSION.SDK_INT >= (Build.VERSION_CODES.TIRAMISU)) {
            ActivityCompat.requestPermissions(
                this, arrayOf(Manifest.permission.POST_NOTIFICATIONS), 0
            )
        }
        setContent {
            // Content
        }
    }
}

Define the permissions in the manifest

<uses-permission android:name="android.permission.FOREGROUND_SERVICE"/>
<uses-permission android:name="android.permission.POST_NOTIFICATIONS" />

Declare the service tag in the manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <!--- Define your permissions ---!>

    <application
        android:name=".MyApplication">
      
        <!-- Other codes -->

        <service
            android:name=".service.StopwatchService"
            android:foregroundServiceType="shortService"
            android:exported="false"/>

    </application>

</manifest>

Initiate start and stop actions from your UI

@Composable
fun CurrentScreen() {

    val context = LocalContext.current

    Column(
        modifier = Modifier.fillMaxSize(),
        horizontalAlignment = Alignment.CenterHorizontally,
        verticalArrangement = Arrangement.Center
    ) {
        Button(onClick = {
            Intent(context,StopwatchService::class.java).also {
                it.action = StopwatchService.Actions.START.toString()
                context.startService(it)
            }
        }) {
            Text(text = "Start Service")
        }
        Button(onClick = {
            Intent(context,StopwatchService::class.java).also {
                it.action = StopwatchService.Actions.STOP.toString()
                context.startService(it)
            }
        }) {
            Text(text = "Stop Service")
        }
    }
}