Is it expected that recomposition will not happen if the `data class` which represents my UI state c...

# compose

[zsperske]

Is it expected that recomposition will not happen if the data class which represents my UI state contains a var and that var changes?

data class EventListState(val events: List<EventUiModel> = emptyList(),
                          var eventDestination: String = "", //Changes to this var do not cause recomposition
                          val pastEventsSelected: Boolean = false,
                          val isLoading: Boolean = true)

[zsperske]

updates happen via this method

fun updateEventDestination(destination: String) {
    val currentState = mutableStateFlow.value
    mutableStateFlow.value = currentState.copy(eventDestination = destination)
}

[CLOVIS]

I'm just a beginner, but I think Compose only detects changes to the State class.

[zsperske]

You can see that I take the current state, and then copy it with the updated state in order to emit a new value

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

Yea, Compose has no way to know if arbitrary properties in classes change, unless they’re backed by snapshot state objects.

[zsperske]

Can you expand on that a little bit? If I update the data class and change that var to a val, then things work as expected

[CLOVIS]

If you use a var, you are editing the object directly. Compose cannot know that.

If you use a val, you can't edit the object, so you edit its reference: if that reference is handled by an object Compose understands (State, StateFlow...) then Compose knows about it

[zsperske]

nice, great explanation! thank you both