I see that `AbstractComposeView`, when creating its composition, looks up the view tree for a `Compo...

# compose

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

I see that AbstractComposeView, when creating its composition, looks up the view tree for a CompositionReference using findViewTreeCompositionReference(). This seems really neat, since it could enable ComposeView -> AndroidView -> … -> ComposeView hierarchies to automatically link their compositions. However, as far as I can tell, AndroidView never actually sets the view tree CompositionReference from the calling composition on its View, and this whole mechanism seems to currently only be used to find the WindowRecomposer.

Would it be feasible for every AndroidView call to get a CompositionReference and set it on its View to support this? Is this sort of automatic linking of compositions across android view subtrees even something that would make sense? If yes, is the AndroidView wiring planned?

https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:compose/ui/ui/src/androidMain/kotlin/androidx/compose/ui/platform/ComposeView.kt;drc=a32c0003449e3ca6141ef497f0ee2759b41943ba;l=176

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

IIRC, at least a couple releases ago, for subcomposition to work the subcomposition had to be manually composed every time the CompositionReference was composed, and so if that’s still the case then this simple view tree mechanism lacks the ability to push those recompose events down and this wouldn’t work.

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

I’m asking because I work on a navigation library where we currently manually implement this sort of nested composition linking through our own, non-view-tag-based mechanism, and it works but it only works if the boundary between compose and android views is controlled by the library. This is a restriction I think we’re ok living with, but if this were something that Compose just supported automatically, it would be great for two reasons: we could delete a bunch of code, and it would work across any Compose/Android view boundaries, not just the ones we control.

[Adam Powell]

hmm, yeah we could do that

[Leland Richardson [G]]

thanks for the idea zach!

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

I think it should be pretty straightforward, i can try to get a CL up probably next week

[Adam Powell]

oh I'm halfway through it now, I'm just writing a test for it

[Adam Powell]

https://android-review.googlesource.com/c/platform/frameworks/support/+/1564002

[Vinay Gaba]

I only read Zach’s comments once (and maybe I should read it a few times) but if I understood this correctly, does this change enable the possibility of introducing a mechanism to propagate recompositions through AndroidView such that ComposeView -> AndroidView -> ComposeView hierarchies have “interlinked” compositions. Does this also come with any performance wins?

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

It doesn’t just enable the possibility of introducing such a mechanism, it is the mechanism.

[zsperske]

great stuff! it's so cool to see such an interactive dev team/community relationship