I do want to filter a SnapshotStateList and than use the filtered list in a LazyColumn. How can i do it? Using this code does not work because it does not detect changes in the list and do not filter the list again:

val list = remember(snapshotStateList) {
    snapshotStateList.filter { removed.contains(it).not() }
}

Not at all related but I'd go for

it !in removed

Hmm, maybe something like:

val filteredList by remember(snapshotStateList, removed) { derivedStateOf { snapshotStateList.filter { it !in removed } }

?

Yes that works. Thank you @Adam Powell But i do not really understand why this works.

derivedStateOf

is kind of like

mutableStateOf

, except it returns a read-only snapshot

State<T>

that always contains the latest value of the lambda expression it was constructed with. It caches the result of this computation. If the derived state block reads other snapshot state, the derived state object will invalidate its cache whenever the state it had to read changes.

ok thx for the explanation 👍

Is original example doesn't work because

snapshotStateList

is mutable, and when SlotTable compares remembered value with new value when

snapshotStateList

changes, it sees no difference, because it's the same object?

yep. (It also doesn't consider the

removed

collection changing.)

Wow, for some reason I assumed

derivedStateOf

didn't need to be remembered. TIL.

so the remember is just in case the referenced object changes right?

Hmm, I'm starting to question @Adam Powell's use of

removed

(and maybe

snapshotStateList

) in the

remember

keys, shouldn't

derivedStateOf

handle that already?

The

derivedStateOf

lambda closes over the collection instances of

snapshotStateList

and

removed

. If the actual collection instances change, we need to create a new

derivedStateOf

to observe those new collections.