Services

1. Giới thiệu

Service là component chạy background, không có UI, thực hiện long-running operations.

2. Loại Services

Type	Description	Thread
Foreground	Visible notification, user aware	Main (cần background thread)
Background	No notification, limited	Main
Bound	Client-server, IPC	Main

3. Foreground Service

Khai báo trong Manifest

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

<service
    android:name=".MusicService"
    android:foregroundServiceType="mediaPlayback"
    android:exported="false" />

Implementation

class MusicService : Service() {

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

    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        val notification = createNotification()

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
            startForeground(
                NOTIFICATION_ID,
                notification,
                ServiceInfo.FOREGROUND_SERVICE_TYPE_MEDIA_PLAYBACK
            )
        } else {
            startForeground(NOTIFICATION_ID, notification)
        }

        // Do work in background thread
        CoroutineScope(Dispatchers.IO).launch {
            playMusic()
        }

        return START_STICKY
    }

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

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

    private fun createNotification(): Notification {
        val channelId = createNotificationChannel()

        return NotificationCompat.Builder(this, channelId)
            .setContentTitle("Playing Music")
            .setContentText("Song name")
            .setSmallIcon(R.drawable.ic_music)
            .setPriority(NotificationCompat.PRIORITY_LOW)
            .build()
    }
}

Start/Stop Service

// Start
val intent = Intent(context, MusicService::class.java)
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    context.startForegroundService(intent)
} else {
    context.startService(intent)
}

// Stop
context.stopService(Intent(context, MusicService::class.java))

4. Bound Service

class DownloadService : Service() {

    private val binder = LocalBinder()

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

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

    fun downloadFile(url: String) {
        // Download logic
    }
}

// Activity binding
class MainActivity : ComponentActivity() {
    private var downloadService: DownloadService? = null
    private var isBound = false

    private val connection = object : ServiceConnection {
        override fun onServiceConnected(name: ComponentName?, service: IBinder?) {
            val binder = service as DownloadService.LocalBinder
            downloadService = binder.getService()
            isBound = true
        }

        override fun onServiceDisconnected(name: ComponentName?) {
            isBound = false
        }
    }

    override fun onStart() {
        super.onStart()
        Intent(this, DownloadService::class.java).also { intent ->
            bindService(intent, connection, Context.BIND_AUTO_CREATE)
        }
    }

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

5. onStartCommand Return Values

Value	Behavior
START_STICKY	Recreate if killed, null intent
START_NOT_STICKY	Don’t recreate
START_REDELIVER_INTENT	Recreate with last intent

6. Service Lifecycle

startService()      →  onCreate() → onStartCommand() → Running → onDestroy()
                                          ↑
startService() again →  ──────────────────┘

bindService()       →  onCreate() → onBind() → Bound → onUnbind() → onDestroy()

7. Service với Coroutines

class MyService : Service() {

    private val job = SupervisorJob()
    private val scope = CoroutineScope(Dispatchers.IO + job)

    override fun onStartCommand(...): Int {
        scope.launch {
            doWork()
        }
        return START_NOT_STICKY
    }

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

8. Android 14+ Restrictions

// Android 14+ cần type cụ thể
<uses-permission android:name="android.permission.FOREGROUND_SERVICE_DATA_SYNC" />
<uses-permission android:name="android.permission.FOREGROUND_SERVICE_LOCATION" />
<uses-permission android:name="android.permission.FOREGROUND_SERVICE_MEDIA_PLAYBACK" />

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📝 Tóm tắt

Khi nào dùng	Solution
Long task, user aware	Foreground Service
Short task	WorkManager
Client-server	Bound Service
Periodic sync	WorkManager