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 lt EventUiModel gt = emptyList var eventDestination String = Changes to this var do not cause recomposition val pastEventsSelected Boolean = false val isLoading Boolean = true ```

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)

👌 1

updates happen via this method

Copy code

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

CLOVIS

08/02/2021, 7:28 PM

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

State

class.

zsperske

08/02/2021, 7:30 PM

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]

08/02/2021, 7:32 PM

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

zsperske

08/02/2021, 7:33 PM

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

08/02/2021, 7:35 PM

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

💯 2

☝🏻 1

zsperske

08/02/2021, 7:43 PM

nice, great explanation! thank you both