I recently added a `LazyListState` property to a view model to preserve the scroll position of a `La...

# compose-android

[Mark]

I recently added a LazyListState property to a view model to preserve the scroll position of a LazyColumn through config changes. However, LeakCanary seems to imply this is causing a memory leak. Any ideas?

[Filip Wiesner]

LazyColumn scroll position should be automatically preserved through it's usage of rememberSaveable 🤔 So putting it in your VM should not be necessary.
Not sure about the leak tho 🤷

[Mark]

Ah yes, you’re right. I was originally playing with having the state in the view model because rememberLazyListState wasn’t working for me, but later realised that was because I was collecting LazyColumn items from a flow where the initialValue was empty and so the state became invalid (0 items). My workaround for this now is to use a dummy state corresponding to when the item state is initialValue . Anyway, the memory leak is now gone, so thanks very much.

[Filip Wiesner]

No worries 🤝 I am glad I could've helped

[Mark]

Hmm, this seems super weird but can this be achieved with something like:

val lazyListState = if (items == null) {
    // use a dummy list state until we get a real items
    rememberLazyListState()
} else {
    rememberLazyListState()
}

[Filip Wiesner]

Ouch 😅 But hey, if it works...

[Mark]

Haha, it seems to…

[shikasd]

For future reports, LeakCanary usually provides a backtrace with fields that caused a leak, which might be useful for debugging.

About lazy list state, you don't really need to recreate state, just scrollToItem whenever items change. It also should work with incorrect indices as well

[Mark]

Thanks Andrei, yes LC pointed me to the LazyListState property in my viewmodel, which is what brought my attention to this. I’m not getting any more LC reports, so it seems fixed now.

The composable collects a flow from the ViewModel so I think there is always going to be a moment where the initialValue is being used. It seems the LazyListState is updated (to item zero) by the LazyColumn when the initial content is empty.