Kotlin Coroutine Android Loader

kotlin_coroutine_android_loader.kt

internal class CoroutineLifecycleListener(private val deferred: Deferred<*>) : LifecycleObserver {
  @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
  fun cancelCoroutine() {
    deferred.cancel()
  }
}

internal var POOL = newFixedThreadPoolContext(2, "loader")

fun <T> LifecycleOwner.load(loader: () -> T): Deferred<T> {
  val deferred = async(context = POOL, start = CoroutineStart.LAZY) { loader() }
  val coroutineLifecycleListener = CoroutineLifecycleListener(deferred)
  lifecycle.addObserver(coroutineLifecycleListener)
  return deferred
}

infix fun <T> Deferred<T>.then(block: (T) -> Unit) = async(context = UI) { block(this@then.await()) }

class MyActivity : AppCompatActivity() {
  lateinit var text: String
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    load {
      "This is an expensive loading..."
    } then {
      text = it
    }
  }
}