LiveData + Kotlin Coroutines

CreateLiveData.kt

package io.github.yaraki.coroutineex

import android.arch.lifecycle.LiveData
import android.content.Context
import kotlinx.coroutines.experimental.Job
import kotlinx.coroutines.experimental.android.UI
import kotlinx.coroutines.experimental.channels.Channel
import kotlinx.coroutines.experimental.channels.SendChannel
import kotlinx.coroutines.experimental.delay
import kotlinx.coroutines.experimental.launch
import kotlinx.coroutines.experimental.yield
import java.io.BufferedReader
import java.io.InputStreamReader
import java.util.concurrent.TimeUnit

fun <E> createLiveData(
        block: suspend SendChannel<E>.() -> Unit
): LiveData<E> {
    return object : LiveData<E>() {

        private var receivingJob: Job? = null
        private var sendingJob: Job? = null

        override fun onActive() {
            super.onActive()
            val channel = Channel<E>()
            receivingJob = launch(UI) {
                for (e in channel) {
                    value = e
                    yield()
                }
            }
            sendingJob = launch {
                channel.block()
            }
        }

        override fun onInactive() {
            super.onInactive()
            sendingJob?.cancel()
            receivingJob?.cancel()
        }
    }
}

fun currentTime() = createLiveData {
    while (true) {
        send(System.currentTimeMillis().toString())
        delay(300L, TimeUnit.MILLISECONDS)
    }
}

fun generateCounter(): LiveData<String> {
    var i = 0
    return createLiveData {
        while (true) {
            send(i.toString())
            i++
            delay(300L, TimeUnit.MILLISECONDS)
        }
    }
}

fun loadText(context: Context, filename: String) = createLiveData {
    BufferedReader(InputStreamReader(context.assets.open(filename))).use { reader ->
        send(reader.readLine())
    }
}

• Finally-clauses in createLiveData are executed at the time of onInactive.
• Variables outside of createLiveData (such as i in generateCounter) are retained as far as the LiveData is retained.