class CustomService : Service() {

//use worker thread if long running operation to not block main UI thread

//or provide some multithreading if needed

private val handlerThread = HandlerThread("HandlerThread")

private lateinit var handler : Handler

override fun onBind(intent: Intent?): IBinder? {

//invokes when bindService called, retrieve intent and decide what to do

//if service is created by bindService and onStartCommand wasn't called then runs only as components are bound

return null //provide communication interface or return null when no bind needed

}

override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {

//invokes when startService or startForegroundService called, retrieve intent and decide what to do

//continues to run until stops itself or by another component

return START_STICKY //restart service strategy after destroyed by the system

}

override fun onCreate() {

//invokes one time setup before onStartCommand or onBind

//not called when service already running

super.onCreate()

handlerThread.start()

handler = Handler(handlerThread.looper)

}

override fun onDestroy() {

//invokes when stopSelf or stopService is called

//service is no longer used or is being destroyed by system or client

super.onDestroy()

handler.removeCallbacksAndMessages(null)

handlerThread.quitSafely()

handlerThread.interrupt()

}

//more lifecycle callbacks

}

//run startService or bindService and pass Intent to run Service