what is the recommended way of achieving callbacks...

# multiplatform

[Alberto]

what is the recommended way of achieving callbacks in Kotlin Multiplatform? Via coroutines?

[zsperske]

are you talking about at the borders of your shared code and platform code?

[Alberto]

For example for interfaces in the common code, that are implemented in platform specific code

[zsperske]

gotcha yeah so if you're using 1.3, coroutines will work fine on Android, but you end up needing to use callbacks on other platforms

[streetsofboston]

We have a KMP supporting Android and iOS.

We have a class called Observer that is in the common shared code and accepts a plain lambda for iOS or a suspend lambda for Android.

These lambdas are the callbacks for `Flow`s emitting data, or, if you want, for a suspend-fun returning a value.

[Alberto]

why needing to use callbacks on other platforms? coroutines don't have an equivalent on iOS for example?

[zsperske]

correct, swift doesn't have a coroutine like facility yet

[Alberto]

are there any samples online around this?

[bsimmons]

This is the setup I use with just pure coroutines. Check out the "Presentation layer" section. Much more flexible than callbacks and I find it cleaner than observers. It also works on iOS well.

[Alberto]

Thanks for sharing. Went over quickly, but mentions "We don’t show any loading indicator, because there’s on big issue: Kotlin/Native does not support multithreading at the moment.
This means, all of our code has to run on the main thread, therefore a loading indicator doesn’t make much sense when we’re doing network on the main thread." - so you're doing everything on main thread on iOS?

[streetsofboston]

There are experimental coroutine lib versions with native mt:
1.3.5-native-mt and a few other versions…., they are mentioned in that 462 issue

[bsimmons]

Oh yeah, I forgot about that. I had to implemented a custom iOS dispatcher with code I lifted from here that will allow async coroutines. Then create your coroutine scopes using that dispatcher.
I'm not sure how the experimental lib works though, as Anton pointed out.

[streetsofboston]

The experimental lib provides the multi-threaded Dispatchers.Default to your common code.

If you are interested in doing KMP for Android and iOS only, take a look at TouchLab’s KaMP-Kit for guidance.

[bsimmons]

^^ yeah, if you can get that working it's for sure better than my hack.

[Peter Hsu]

so does 1.3.5-native-mt actually provide multithreading on iOS? i couldn't find any documentation on the release and have been reading through github for a while trying to figure it out

[russhwolf]

There's documentation within the branch at https://github.com/Kotlin/kotlinx.coroutines/blob/native-mt/kotlin-native-sharing.md

[Peter Hsu]

cool, so it sounds like at least some basic ability to run coroutines on a background thread is supported on all platforms with Dispatchers.Default implemented, with the caveat that it's currently a single background thread.. does that sound right?

[russhwolf]

Also with the caveat that it doesn't rescue you from needing to handle things getting frozen when crossing threads

[Peter Hsu]

thanks, that's very helpful

[Peter Hsu]

and what does 1.4.0-mt add?

[russhwolf]

1.4 support and whatever bugs they've fixed in the meantime. If you want more detail you're mostly stuck digging through issues and commit messages (or looking at the code directly)

[Peter Hsu]

yeah, i've been doing that quite a bit, was hoping to get my head out of the weeds to see if someone could help at a higher level.