使用属性作为 Kotlin 协程的访问器

Question

Kotlin Coroutines question... struggling w/ using a property instead of a function being the accessor for an asynchronous call.

Background is that I am trying to use the FusedLocationProviderClient with the kotlinx-coroutines-play-services library in order to use the .await() method on the Task instead of adding callbacks...

Currently having a property getter kick out to a suspend function, but not sure on how to launch the coroutine properly in order to avoid the

required Unit found XYZ

error...

 val lastUserLatLng: LatLng?
        get() {
            val location = lastUserLocation
            return if (location != null) {
                LatLng(location.latitude, location.longitude)
            } else {
                null
            }
        }

    val lastUserLocation: Location?
        get() {
            GlobalScope.launch {
                return@launch getLastUserLocationAsync()  <--- ERROR HERE
            }
        }

    private suspend fun getLastUserLocationAsync() : Location? = withContext(Dispatchers.Main) {
        return@withContext if (enabled) fusedLocationClient.lastLocation.await() else null
    }

Any thoughts on how to handle this?

Answer 1

Properties can't be asynchronous. In general you should not synchronize asynchronous calls. You'd have to return a Deferred and call await() on it when you need a value.

val lastUserLatLng: Deferredd<LatLng?>
    get() = GlobalScope.async {
        lastUserLocation.await()?.run {
            LatLng(latitude, longitude)
        }
    }

val lastUserLocation: Deferred<Location?>
    get() = GlobalScope.async {
        getLastUserLocationAsync()
    }

private suspend fun getLastUserLocationAsync() : Location? = withContext(Dispatchers.Main) {
    return@withContext if (enabled) fusedLocationClient.lastLocation.await() else null
}

But technically it's possible, though you should not do it. runBlocking() blocks until a value is available and returns it.