``` val downloadFlow = flow { var read = 0 while (read < total) { ...

# coroutines

[mbonnin]

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.

[streetsofboston]

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

[mbonnin]

Ah, alright, withContext(<http://Dispatchers.IO|Dispatchers.IO>) works from flow{} as long as we don't emit from ?

[mbonnin]

Yep, looks like it, thanks !

[mbonnin]

I also just bumped into flowOn that looks promising...