Hi! I’m practicing Compose for desktop and I’m stuck with the problem: I have “screenState: StateFlo...

# compose-desktop

[Semyon Zadorozhnyi]

Hi! I’m practicing Compose for desktop and I’m stuck with the problem:
I have “screenState: StateFlow” value with state for my UI (sealed class)
From UI I use default approach “screenState.collectAsFlow()” to trigger recomposition if state changes
and I have method “subscribe(chatRoom: ChatRoom)” in my ApplicationController (aka view model for desktop)
which calls to a useCase and returns Flow<Message>. Emitter takes my state and makes a copy with a new message but from time to time Compose ignores (or misses) new state value.
Screenshots in thread.

[Semyon Zadorozhnyi]

Compose state

[Semyon Zadorozhnyi]

State flow in app controller

[Semyon Zadorozhnyi]

chat message emitter

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

You need to copy the list as well, or use SnapshotStateList

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

Some other notes:
1. It’s considered a bad practice to implement CoroutineScope directly from classes that do other things. Store the scope in a property instead (elizarov has written about this).
2. No need to pass Dispatchers.Main to collectAsState, it will use the compose dispatcher by default (which is basically Dispatchers.Main with extra features).
3. There’s a potential data race in your subscribe coroutine, if there are multiple instances of that coroutine running concurrently. One way to fix would be wrap the body of the collect with a Mutex.

[Semyon Zadorozhnyi]

Noted)
Problem solved, thanks a lot!

No need to pass Dispatchers.Main to collectAsState

That’s just attempt to fix the problem by changing something random 😄