서비스

참조
https://developer.android.com/guide/components/services

1. start 서비스
   startService를 통해 서비스를 시작하면 onStartCommand()가 호출됨.
   종료할때는 stopSelf() 혹은 stopService()

2. bound 서비스
   bindService를 통해 IBinder를 반환.
   모든 클라이언트로 부터 바인딩이 해제되면 시스템은 서비스를 소멸시킴.

서비스는 기본스레드에서 실행됨.
서비스에서 시간이 많이 소요되는경우 스레드 생성해서 실행하는게 좋다.

1. manifest에 선언

<manifest ... >
  ...
  <application ... >
      <service android:name=".ExampleService" />
      ...
  </application>
</manifest>

android:exported 특성을 통해 자신의 앱에만 사용가능여부를 나타낼수있다.

2. Service 클래스 구현

class HelloService : Service() {

    private var serviceLooper: Looper? = null
    private var serviceHandler: ServiceHandler? = null

    // Handler that receives messages from the thread
    private inner class ServiceHandler(looper: Looper) : Handler(looper) {

        override fun handleMessage(msg: Message) {
            // Normally we would do some work here, like download a file.
            // For our sample, we just sleep for 5 seconds.
            try {
                Thread.sleep(5000)
            } catch (e: InterruptedException) {
                // Restore interrupt status.
                Thread.currentThread().interrupt()
            }

            // Stop the service using the startId, so that we don't stop
            // the service in the middle of handling another job
            stopSelf(msg.arg1)
        }
    }

    override fun onCreate() {
        // Start up the thread running the service.  Note that we create a
        // separate thread because the service normally runs in the process's
        // main thread, which we don't want to block.  We also make it
        // background priority so CPU-intensive work will not disrupt our UI.
        HandlerThread("ServiceStartArguments", Process.THREAD_PRIORITY_BACKGROUND).apply {
            start()

            // Get the HandlerThread's Looper and use it for our Handler
            serviceLooper = looper
            serviceHandler = ServiceHandler(looper)
        }
    }

    override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int {
        Toast.makeText(this, "service starting", Toast.LENGTH_SHORT).show()

        // For each start request, send a message to start a job and deliver the
        // start ID so we know which request we're stopping when we finish the job
        serviceHandler?.obtainMessage()?.also { msg ->
            msg.arg1 = startId
            serviceHandler?.sendMessage(msg)
        }

        // If we get killed, after returning from here, restart
        return START_STICKY
    }

    override fun onBind(intent: Intent): IBinder? {
        // We don't provide binding, so return null
        return null
    }

    override fun onDestroy() {
        Toast.makeText(this, "service done", Toast.LENGTH_SHORT).show()
    }
}