Hi! I’m practicing Compose for desktop and I’m stu...

# compose

[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 in the application controller

[Semyon Zadorozhnyi]

collector

[Semyon Zadorozhnyi]

_screenState.value = current.copy(messages = updatedList)
Is being triggered every time, but there is no recomposition sometimes

[Nat Strangerweather]

You might want to try and ask here: #compose-desktop

[Filip Wiesner]

StateFlow emits only "new" values based on equality so make sure you don't emit the same instance. In addition to that StateFlow conflates emits if they happen too quickly but it should always emit the latest value.

[Semyon Zadorozhnyi]

I believe that .copy() creates new reference but I'll check it anyway

Not the second one for sure. First state after default is always missing.

[Filip Wiesner]

Copy does create new instance but maybe equals method returns true. Is ScreenState data class?

[Semyon Zadorozhnyi]

@Filip Wiesner ScreenState is sealed, but underlying class with list of messages is indeed "data" class.

[Semyon Zadorozhnyi]

[Semyon Zadorozhnyi]

Seems like state.value is working nice because if I change “val text: String” right after new message is set - recompose happens and I see the new message. But message should be visible right after “Enter” pressed

[Filip Wiesner]

As a general rule state should never be mutable. Try creating new messages (non-mutable) list for each InRoom state change because I still think the problem is in the equality method. Or maybe swap StateFlow for SharedFlow.

[Filip Wiesner]

Oh, I see you solved your problem in #compose-desktop ✅

[Semyon Zadorozhnyi]

Yep, seems like List can affect state change. Thank you for help!