Is it possible to connect to the service if the…

Yes, it is possible using Context and Binding.

Create a Service: Extend from Service (or IntentService/JobIntentService). Implement onBind(Intent intent) which returns an IBinder.

class MyBoundService : Service() {

    private val binder = MyBinder()

    inner class MyBinder : Binder() {
        fun getService(): MyBoundService = this@MyBoundService
    }

    override fun onBind(intent: Intent): IBinder {
        // Return IBinder for client interaction
        return binder
    }
}

Bind from an Activity: Use Context.bindService(). Implement ServiceConnection.

class MyActivity : AppCompatActivity() {

    private var myService: MyBoundService? = null
    private var isBound = false

    private val connection = object : ServiceConnection {
        // Called when connection is established
        override fun onServiceConnected(className: ComponentName, service: IBinder) {
            val binder = service as MyBoundService.MyBinder
            myService = binder.getService()
            isBound = true
            // Now myService is available and its methods can be called
        }

        // Called when connection is unexpectedly lost
        override fun onServiceDisconnected(arg0: ComponentName) {
            isBound = false
            myService = null
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // ...
        bindService(Intent(this, MyBoundService::class.java), connection, BIND_AUTO_CREATE)
    }

    override fun onDestroy() {
        super.onDestroy()
        if (isBound) {
            unbindService(connection)
            isBound = false
        }
    }
}

When calling bindService with the flag BIND_AUTO_CREATE, if the service is not already running, it will be created. The Activity will be connected to it after creation. onServiceConnected in ServiceConnection will be called once the service is fully initialized and ready.

It is important to properly manage the lifecycle of the binding by calling unbindService in the appropriate lifecycle method of the Activity (e.g., onDestroy or onStop / onPause, depending on the required logic).

Is it possible to connect to the service if the Activity is started after it?