LiveData + Kotlin Coroutine

AsyncLiveData.kt

// compile "org.jetbrains.kotlinx:kotlinx-coroutines-android:0.16"
// compile "android.arch.lifecycle:runtime:1.0.0-alpha3"
// compile "android.arch.lifecycle:extensions:1.0.0-alpha3"
// kapt "android.arch.lifecycle:compiler:1.0.0-alpha3"

class AsyncLiveData<T> private constructor(private val exec: suspend () -> T) : LiveData<T>() {

    private var observer: Observer<T>? = null

    private var job: Job? = null

    companion object {
        fun <T> create(exec: suspend () -> T): AsyncLiveData<T> {
            return AsyncLiveData(exec)
        }
    }

    override fun observe(owner: LifecycleOwner?, observer: Observer<T>?) {
        super.observe(owner, observer)
        this.observer = observer
    }

    override fun onActive() {
        super.onActive()

        job = launch(UI) {
            val result = async(context + CommonPool) {
                exec()
            }.await()

            value = result

            removeObserver(observer)
        }
    }

    override fun onInactive() {
        super.onInactive()
        job?.cancel()
    }
}

Usage.kt

AsyncLiveData.create {
    delay(3000)
    1 + 2
}.observe(owner, Observer {
    Log.d("AsyncLiveData", "$it")
})

// log
// D/AsyncLiveData: 3