Implementation to make it easier to manage Composition of RxJava 2 using LifecycleObserver of Android Architecture Component and Delegate of Kotlin

RxJava2LifecycleObserver.kt

/* Interface is necessary for Delegate */
interface RxJava2LifecycleDelegate {
  fun Disposable.autoDispose(): Disposable
  fun Lifecycle.setupRxJava2Observer(func: () -> Unit)
}

/* Class for Delegate implementing LifecycleObserver */
class RxJava2LifecycleDelegateImpl : RxJava2LifecycleDelegate {
  private var composite = CompositeDisposable()

  /**
   * Extension function for registering LifecycleObserver and subscribe method
   * @func: This lambda calls subscription processing
   */
  override fun Lifecycle.setupRxJava2Observer(func: () -> Unit) {
    addObserver(RxJava2LifecycleObserver(composite, func))
  }

  private fun check() {
    if (composite.isDisposed) {
      composite = CompositeDisposable()
    }
  }

  /* Extension function for composite management of Disposable  */
  override fun Disposable.autoDispose(): Disposable {
    check()
    composite.add(this)
    return this
  }
}

class RxJava2LifecycleObserver(private val composite: CompositeDisposable,
                               private val subscribeCallback: () -> Unit)
  : LifecycleObserver {

  /* It is automatically called at onResume timing and sets up subscription processing. */
  @OnLifecycleEvent(Lifecycle.Event.ON_START)
  fun subscribe() {
    subscribeCallback()
  }

  /* It is automatically called at the timing of onPause and releases subscription processing. */
  @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
  fun dispose() {
    composite.dispose()
  }
}

/* Example Implementation */
class ExampleActivity : AppCompatActivity(), RxJava2LifecycleDelegate by RxJava2LifecycleDelegateImpl() {

  override fun onCreate(savedInstanceState: Bundle?) {
    ...
    // Register the Observer to subscribe onResume and dispose with onPause
    lifecycle. setupRxJava2Observer(this::subscribes)
  }
  
  /* subscribe method */
  private fun subscribes() {
    //subscribe example
    vm.progress.subscribe {
      if (it) showProgress() else dismissProgress()
    }.autoDispose() //Monitor disposable
   ...
  }
}