Why does this keeps recomposing

Button

slot's content and printing "recomposing"?

MaterialTheme {
  val handler = { _: TextLayoutResult -> }
  MyButton(handler)
}

@Composable
fun MyButton(handler: (TextLayoutResult) -> Unit) {
  val state by flowOf("two", "three").collectAsState("one")
  Button(onClick = {}, enabled = state == "two") {
    println("recomposing content")
    Text(text = "Button", onTextLayout = handler)
  }
}

If I remove "handler" parameter recomposition happens only once. Is there a way to somehow mark "handler" as stable?

Try using

remember { flowOf("two", "three") }.collectAsState("one")

?

ohh, right. I was investigating a weird recomposition which happens if I pass a lambda into a slot. Tried to come up with a minimal example and produced a compromised one 🙂 Will try further. In my case state flow is not recreated — for sure

I am not sure if a lambda supports

equal

. I think, setting a lambda variable inside a recomposition is not supported.

But lambda is an object, so

handler == hanlder

will be

true

If the dependencies of a lambda didn’t change, the same lambda instance will be used so it

equals()

the previous one.

In my latest sample above lambda is the same, but it still recomposes for some reason. this happens even if I modify sample to pass

() -> Unit

lambda to some

onClick

inner to the slot.

can you check if compose marks it as

@Stable

? https://github.com/androidx/androidx/blob/androidx-main/compose/compiler/design/compiler-metrics.md

Oh, nice hint, thanks! I'll try to use this, heard of it, will read up. I hope it works with 1.1.x compose

yep we use the metrics with 1.1.x of compose

I think lambdas should be optimized in that case to keep the same instance (it doesn't capture any values) About flow, and collecting as state, I believe you restart it on every composition, because you remembered flow, and not resulting state, resulting in re-subscription to flow and recomposition as state updates each time. Most likely, you are looking for:

remember { flowOf(...).collectAsState("one") }

Note that state is created inside remember in that case.