Android LiveData / architecture components integration

We need an integration module for Android LiveData architecture components that provides read-to-use extensions for their use with coroutine in a similar style to reactive integration modules. See also #232

[dmytrodanylyk]

Uploaded to github working android sample.

• library
• example-live-data based on developer.android.com

[dmytrodanylyk]

@elizarov

Me and Andras wanted to share some progress on coroutines + arch work. Let’s speak about LiveData first, as it is most used component which is used in Room and ViewModel.

Our initial idea was to wrap LiveData with ConflatedBroadcastChannel which basically act the same. But implementation is error prone and may not reflect all the future changes which google may make.

So we decided to implement it in different way.

import android.arch.lifecycle.Observer
import android.arch.lifecycle.LifecycleObserver

class LiveDataChannel<T>(private val liveData: LiveData<T>)
    : LinkedListChannel<T?>(), SubscriptionReceiveChannel<T?>, Observer<T?>, LifecycleObserver {

    override fun onChanged(t: T?) {
        offer(t)
    }

    override fun afterClose(cause: Throwable?) = liveData.removeObserver(this)

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun onDestroy() = close()

}

fun <T> LiveData<T>.observeChannel(lifecycleOwner: LifecycleOwner): LiveDataChannel<T> {
    val channel = LiveDataChannel(this)
    observe(lifecycleOwner, channel)
    lifecycleOwner.lifecycle.addObserver(channel)
    return channel
}

fun <T> LiveData<T>.observeChannel(): LiveDataChannel<T> {
    val channel = LiveDataChannel(this)
    observeForever(channel)
    return channel
}

Basically you subscribe to LiveData but as a return type get Channel, not an Observable.

Usage sample:

val channel = liveData.observeChannel(lifecycleOwner)
launch {
    channel.consumeEach { data: List<Data>? ->
        // use data
    }
}

This is a nice way to bridge LiveData - Channels.