Hi there, I have done some testing, regarding ComposeView.setContent and entering a new composition:...

# compose-android

[uli]

Hi there,
I have done some testing, regarding ComposeView.setContent and entering a new composition:

fun setupCompose(val value: Int) {
    composeView.setContent {
        LaunchedEffect(kotlin.Unit) {
            println("Uli: Effect Launched")
        }
        MyValueView(value)
    }
}

var myValue = 0
repeat(10) { setupCompose(myValue++) }

I was suspecting the effect to fire 10 times, as the composable is being setup from scratch. Well, it didn’t. It fired only once.
Now I am wondering, if anything, could break the optimization and actually lead to the effect firing 10 times, or if I can rest assured that resetting the composeView’s content does not enter a new composition

[Pablichjenkov]

Why would you expect that?
The Effect lambda just copy whatever it references once and survive across recompositions. You need to key it if you want to update.

[Pablichjenkov]

Kinda similar behavior as remember

[uli]

i was expecting that when I pass a new lambda into setContent, it would start from scratch

[Pablichjenkov]

For that you have SideEffect which executes per recomposition but LaunchEffect runs only once when the Composable enters the composition tree

[uli]

And I was thinking, setContent would make it enter the composition again. I.e. remove it and insert it.

[Pablichjenkov]

If you reference State inside LaunchEffect is a good practice use it as key

[uli]

@Pablichjenkov, thanks, I am aware of that. I did the tests more for optimization and thought I should not call setContent multiple times. I am postively surprised, that the effect is called only once

[Pablichjenkov]

I got you now, I was actually thinking of setContent as a general example not the real one. In this case my theory is that once the composer tree starts, whatever update it receives later it will continue diffing it against whatever it had before, if there was anything. It won't fully update but keeps diffing as any other composable function. The set part in the name is probably misleading i guess

[uli]

thx

[Albert Chang]

I believe it's because you are setting the content in the same frame. Composition won't start until a new frame.

[uli]

Same if I put delay(1000) between

[uli]

But good catch

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

I’m not sure if it’s part of setContent’s contract that it doesn’t create a brand new composition. But if you need that strong guarantee, just use AbstractComposeView. Then you implement an abstract method to define your composable, and can implement that guarantee yourself.