val downloadFlow = flow {
            var read = 0
            while (read < total) {
                read += readFromNetwork() // How do I make this run from a background thread ? <http://Dispatcher.IO|Dispatcher.IO> or other ?
                emit(read to total)
            }
        }

        downloadFlow.collect {
            // this should run from the main thread
            displayProgress(it)
        }

What would be the idiomatic way to have a long running background operation emit progress that is read from the main thread ? The

flow

doc explicitely prohibits changing context in the flow block.

For polling, as you do here, by calling

readFromNetwork

repeatedly, you can make

readFromNetwork

a

suspend

fun and run it on a background thread (e.g.

suspend fun readFromNetwork() = withContext(<http://Dispatchers.IO|Dispatchers.IO>) { ... }

. For callback, you use

channelFlow

or

callbackFlow

instead of plain

flow

Ah, alright,

withContext(<http://Dispatchers.IO|Dispatchers.IO>)

works from

flow{}

as long as we don't

emit

from ?