[Android] LifecycleObserver

LifecycleObserver

설명

• Activity의 onCreate, onDestroy와 같은 생명 주기 메소드를 별도로 분리하여 Activity 코드를 간결하게 유지할 수 있도록 해주는 클래스
• background, foreground 상태 체크를 위해서 Application에 LifecycleObserver를 적용할 수 있다.

Activity에 적용하는 예제

ActivityLifecycleObserver

class ActivityLifecycleObserver(private val lifecycle: Lifecycle) : LifecycleObserver {
    companion object {
        const val TAG = "[DEBUG]"
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    fun onCreated(source: LifecycleOwner) {
        Log.d(TAG, "onCreated")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun onStart() {
        Log.d(TAG, "onStart")
        if (lifecycle.currentState.isAtLeast(Lifecycle.State.INITIALIZED)) {
            Log.d(TAG, "currentState is greater or equal to INITIALIZED")
        }
        if (lifecycle.currentState.isAtLeast(Lifecycle.State.CREATED)) {
            Log.d(TAG, "currentState is greater or equal to CREATED")
        }
        if (lifecycle.currentState.isAtLeast(Lifecycle.State.STARTED)) {
            Log.d(TAG, "currentState is greater or equal to STARTED")
        }
        if (lifecycle.currentState.isAtLeast(Lifecycle.State.RESUMED)) {
            Log.d(TAG, "currentState is greater or equal to RESUMED")
        }
        if (lifecycle.currentState.isAtLeast(Lifecycle.State.DESTROYED)) {
            Log.d(TAG, "currentState is greater or equal to DESTROYED")
        }
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    fun onResume() {
        Log.d(TAG, "onResume")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    fun onPause() {
        Log.d(TAG, "onPause")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun onStop() {
        Log.d(TAG, "onStop")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun onDestroy() {
        Log.d(TAG, "onDestroy")
    }
}

MainActivity

class MainActivity : AppCompatActivity() {
    private var observer = ActivityLifecycleObserver(lifecycle)

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        lifecycle.addObserver(observer)
    }
}

Application에 적용하는 예제

build.gradle

dependencies {
    ....
    implementation "android.arch.lifecycle:extensions:1.1.1"
}

ApplicationLifecycleObserver

class ApplicationLifecycleObserver : LifecycleObserver {
    companion object {
        const val TAG = "[DEBUG]"
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun onForeground() {
        Log.d(TAG, "onForeground")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun onBackground() {
        Log.d(TAG, "onBackground")
    }
}

AppApplication

class AppApplication : Application() {
    override fun onCreate() {
        super.onCreate()

        ProcessLifecycleOwner.get().lifecycle.addObserver(ApplicationLifecycleObserver())
    }
}

AndroidManifest.xml

<application ... android:name=".AppApplication">...</application>

참고

• https://developer.android.com/jetpack/androidx/releases/lifecycle?hl=ko
• https://codechacha.com/ko/android-jetpack-lifecycle/
• https://blog.kmshack.kr/ProcessLifecycleOwner%EB%A5%BC-%EC%9D%B4%EC%9A%A9%ED%95%9C-%EC%95%B1-Background,-Foreground-%EC%9D%B4%EB%B2%A4%ED%8A%B8-%EC%B2%98%EB%A6%AC/