I recently made a very simple comic viewer app for...

# compose

[Md. Nazmun Sadat Khan]

I recently made a very simple comic viewer app for XKCD using Jetpack compose. However, my composables are too big, with lots of complicated business logic in it, launching lots of coroutines etc.

I am thinking of making a custom state object inside which I am going to move all the business logic, leaving only the UI parts to the composable functions.

Is it ok to launch composables from within state classes?

[Adam Powell]

The phrasing of, "launch composables from within state classes" confuses me a bit, but I occasionally write state objects with suspend methods that keep updates/ongoing behavior running, and then have a composable do something like

@Composable
fun Thing(state: ThingState) {
  LaunchedEffect(state) {
    state.keepUpdated()
  }
  // ...
}

[Adam Powell]

This tends to make unit testing ThingState really smooth

[Md. Nazmun Sadat Khan]

My question was, to use your example, should I make state.keepUpdated a suspend function and launch the coroutine from the composable, or is it better to make state.keepUpdated a regular function and launch the coroutine inside the method.

[Adam Powell]

What scope would you launch it in/where would you call the launcher method?

[Md. Nazmun Sadat Khan]

Still a newbie so haven't thought about the details through, but I am currently using a CoroutineScope via rememberCoroutineScope in my composables.

[Adam Powell]

Definitely don't raw launch from a @Composable - it's one thing if it's in a click handler or something but composables are transactional and launching is a side effect that needs to be controlled to only escape composition if composition successfully commits

[Adam Powell]

This is what LaunchedEffect does for you

[Md. Nazmun Sadat Khan]

It was for a click handler

[Md. Nazmun Sadat Khan]

All in all, I think your approach is better. Create a custom state class, create suspend methods and let the composable decide the scope.

[Adam Powell]

Yeah if you have to provide a scope to the state object things get a lot more complicated

[Adam Powell]

This sort of thing is also why things like MutatorMutex exist; we encountered a lot of cases where a new actor in this kind of capacity needed to be able to kick out an old one

[Md. Nazmun Sadat Khan]

Ok thanks for pointing me in the right direction.

[Adam Powell]

I'm not entirely sure it's the right direction yet, but I hope it's been a helpful direction to think in and I'm curious to see what you arrive at 🙂