Services

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Services Deep Dive

Overview

A Service is an Android component used for background work that should continue independently of UI screens. Services do not provide UI and are managed by the system with their own lifecycle.

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Service Types

Started Service

• Started with startService() or startForegroundService().
• Runs until stopSelf()/stopService() is called.
• Good for one-off background tasks.

Bound Service

• Started with bindService().
• Exposes APIs via IBinder.
• Runs while clients are bound (unless also started).
• Useful for in-process or cross-process IPC.

Foreground Service

• Must show persistent notification.
• Higher priority, less likely to be killed.
• Required for user-visible long-running tasks.

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Lifecycle

Started Service Flow

override fun onCreate() {
    super.onCreate()
}

override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
    // Do work off main thread
    return START_NOT_STICKY
}

override fun onDestroy() {
    super.onDestroy()
}

Restart Modes

• START_NOT_STICKY: Do not recreate after kill.
• START_STICKY: Recreate service, intent may be null.
• START_REDELIVER_INTENT: Recreate and redeliver last intent.

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Service vs Thread

• Thread: execution unit, tied to process lifetime.
• Service: component managed by Android lifecycle.
• Service work still needs threading (Dispatchers.IO, Executor, etc).

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Bound Service Example

class PlayerService : Service() {
    private val binder = LocalBinder()

    inner class LocalBinder : Binder() {
        fun getService(): PlayerService = this@PlayerService
    }

    override fun onBind(intent: Intent?): IBinder = binder

    fun play(trackId: String) {
        // business logic
    }
}

private val connection = object : ServiceConnection {
    override fun onServiceConnected(name: ComponentName?, service: IBinder?) {
        val binder = service as PlayerService.LocalBinder
        val playerService = binder.getService()
        playerService.play("track_1")
    }

    override fun onServiceDisconnected(name: ComponentName?) = Unit
}

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Android 8+ Background Limits

• Background service starts are restricted.
• Use startForegroundService() when required.
• Prefer WorkManager for deferrable background work.

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Interview Traps

• Service does not run on a separate thread by default.
• Foreground service requires notification promptly.
• IntentService is deprecated; use WorkManager.

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Key Takeaways

• Services represent background-capable components, not threading primitives.
• Choose started, bound, or foreground based on interaction and visibility.
• Use modern background APIs (WorkManager) for resilient scheduling.