So, I have some code that basically boils down to ...

# compose

[s3rius]

So, I have some code that basically boils down to this:

class State {
	var item by mutableStateOf<IClass?>(null)
}

@Composable
fun SomeUi(state: State) {
	Text("Item is ${state.item}")
}

SomeUi() is rendered to screen, and state.item is changed from null to some value a little afterwards. But SomeUi never picks up on that update and thus the text keeps saying "Item is null". But the way I understand the Compose state system, this should work fine, shouldn't it?

I can verify that state.item does change its value (by just periodically printing it in a coroutine). What's odd is that if I experimentally change IClass? to String? it works again.

I want to put more effort into debugging it, but first I'd like to verify that I'm not simply misunderstanding something about State and how it's supposed to work.

[Rafs]

Where are you calling SomeUI from?

[s3rius]

Nothing special. Some other composable, and eventually a top-level composable.

Boiled down, it's basically like this:

application {
	val state = remember { State() } 
	LaunchedEffect(Unit) { // just an example
		delay(100)
		state.item = getMeSomeItem()
	}
	SomeUi(state)
}

The real code is much more involved, but conceptually it's this.

Edit: added the remember { }

[Rafs]

You should remember your state.
val state = remember{ State() }

[s3rius]

Sorry, my bad! Yes, it is remembered.

[Rafs]

I just tried this and it worked

[s3rius]

Yeah, I couldn't reproduce it either. Simple examples work, but I can see that the problem exists in my codebase. That's why I can't give a reproducer for the problem.

Hence my question of whether this should work or not. I thought, maybe I overlooked a requirement like a stability guarantee for state or item, or something else.
For example if someone had told me "Yeah your State needs to be @Stable for this to work" I could have stopped debugging the problem. But if the answer is "No, this should always work" then I have to do more in-depth debugging to pin point the reason why it doesn't work in this case.

[s3rius]

But thank you for taking the time to write the reproducer! I appreciate it.

[Zach Klippenstein (he/him) [MOD]]

Yep that definitely should work, as written