I have a ComposeView in a Fragment, that doesn't get it's state restored when from popping the back stack for a fragment transaction. I've tried using an XML with an id set on the ComposeView which normally would save view state for non-compose views. This is resetting my LazyColumn position to the top. I can work around it by having a LazyListState in the Fragment ViewModel. Having to save all view state in the VM to be restored when popping the back stack doesn't seem optimal. Am I doing something wrong?

Are you setting the right ViewCompositionStrategy on your ComposeView? https://kotlinlang.slack.com/archives/CJLTWPH7S/p1619714525127100?thread_ts=1616835899.254600&cid=CJLTWPH7S

I'll look into that. I made a test app that just did a fragment transaction and it does save the LazyColumn state. I'm losing the ComposeView state when using NavComponent to navigate to another view and popping back.

I know @Manuel Vivo was looking at that exact page just recently. Yes, you should always be using

ViewCompositionStrategy.DisposeOnViewTreeLifecycleDestroyed

when in a fragment

I thought NavComponent uses fragment transactions under the hood. I confused why I need to change the composition strategy using NavComponent but not when doing a simple fragment transaction.

It absolutely does use fragment transactions, that's the only way to interact with fragments

And it gets a lot more complicated when it comes to running animations and transitions - that's really where the issues come in. Does your Navigation code use those / are you using NavigationUI?

Yes, my nav component does animations.

Add animations to your fragment transaction and you'll see the same behavior

I tried a transaction with an animation and it did save the ComposeView's state when popping.

Ah, sorry, I should have been more clear - in the View system, there's two entirely, completely separate systems -

Animation

(introduced in API 1, what you're using) and

Animator

(introduced in API 11 as a replacement for

Animation

which is what Navigation, Transitions, and everything else uses).

Animator

is the only one that does the detaching behavior.

I see. NavComponent action enterAnim etc use Animator. I thought it would use Animation.

Ah no, there's a number of infeasible to fix problems with

Animation

that make it a terrible choice in general

Yeah, I saw an IO talk about all the different animation systems. I'd need to rewatch it to refresh my memory.

Thanks for raising this, yeah, I’m updating the docs to include this. In fact, Ian has an email in his inbox regarding this 😄