I want to observe recomposition using prints, but ...

# compose

[marcinmoskala]

I want to observe recomposition using prints, but it seems they are not perfectly reliable. If I use a print in a body, it is sometimes not called even if this function got recomposed. For instance here, ChatTopBar gets recomposed unnecessarily because List is not stable, and I can see in Layout Inspector that it gets recomposed, but this print is only executed during the initial composition phase. Do you know what might be the reason why it works this way? I can provide a complete example.

@Composable
fun ChatTopBar(messages: List<Message>) {
    println("ChatTopBar recomposition")
    TopAppBar(title = {
        println("TopAppBar title recomposition")
        Text("Messages ${messages.size}")
    })
}

[Stylianos Gakis]

Each composable may have many different recomposition scopes, and each may be recomposing in different frequencies than others.
If your print lives in a recomposition scope which simply gets skipped, it will not print anything.

[marcinmoskala]

Not sure what you mean. Even if they have different scope, if ChatTopBar gets recomposed, it should execute its body, so execute print, or am I wrong?

[Stylianos Gakis]

Yeah but println("ChatTopBar recomposition") and println("TopAppBar title recomposition") live in different recomposition scopes, provided TopAppBar is not inline

[marcinmoskala]

My problem is that I know ChatTopBar should get recomposed due to List not being stable (it hasn't changed, but it is unstable, so it should trigger recomposition), and I can see that it gets recomposed in Layout Manager, but print does not seem to be called.

[marcinmoskala]

Yes, but they both print to the same console, no?

[Stylianos Gakis]

Do you have strong skipping enabled? It may be skipping List anyway if it's equal referentially

[marcinmoskala]

This is a new project and I assumed it is not set by default, I will check it now

[Stylianos Gakis]

It is on by default in the latest compose versions

[marcinmoskala]

o.0

[marcinmoskala]

Thanks for letting me know, I missed that, and that is important

[marcinmoskala]

Yes, this was the problem, when I explicitly disabled it, now everything gets recomposed and prints work as I expected

[marcinmoskala]

Documentation should be updated

[Stylianos Gakis]

https://developer.android.com/develop/ui/compose/performance/stability/strongskipping
Looks to be updated atm

[Pablichjenkov]

Also, if you are sure it recomposed because the layout inspector but you don't see the printed text. Then you might be a victim of " doughnut hole skipping"
https://www.jetpackcompose.app/articles/donut-hole-skipping-in-jetpack-compose

[shikasd]

If layout inspector is showing this function as recomposed when it actually didn't, it sounds like a bug