how do you approach updating the view model during...

# android

[Bruno_]

how do you approach updating the view model during long running tasks? I have to crawl data from ~20 websites and display it as a list.
Do I:
• make an update publisher (new items are being pushed into it)
• refresh the view model data every let's say 1s
• try to implement it so that if the user get's to the end of the list, more items are loaded

[atlantis210]

I'd say that if it takes much time it means it is not the best approach to display it on screen. You'll have to rethink your screen. Maybe make a viewpager and display each data retrieved from each site on a single page...
Otherwise, if you really want to do what you said, I suggest you use PagedList and update your item's list with LiveData each time an item is available

[kyleg]

Sounds like a job for MediatorLiveData. Suppose you have 10 websites to crawl.

data class Website(val url: String)

val sitesToCrawl: List<Website> = TODO()

fun crawl(url: String): LiveData<List<PageData>> = TODO()

val observer = MediatorLiveData<List<PageData>>().apply { value = list() }

sitesToCrawl.forEach { site ->
  val ld = crawl(site.url)
  observer.addSource(ld) { list ->
    observer.value = observer.value+list
  }
}

Something like that. Can’t remember if I’m doing list concat correctly.

[kyleg]

The approach with something like ArrowFx is similar and doesn’t require Android libraries.

[Bruno_]

@atlantis210 it's doesn't take a lot of time to load, it's just I'm new to android and I don't know how to solve the problem, currently I use the first approach
these tasks are long running but they are not blocking the main thread

@forward many thanks for the tip, I didn't know about this class, will make use of it