I've read Zach K blog posts on the topic but I'm still encountering a situation that I can't seem to...

# compose

[Colton Idle]

I've read Zach K blog posts on the topic but I'm still encountering a situation that I can't seem to untangle. Essentially I have a list of items. This list is a mutableStateList. Every item could also have a single property that is also mutableState. When I update this item mutableState, I don't see the composable recompose. Can anyone spot any egregious issues here?

class ScreenViewState {
  val list = mutableStateListOf<Item>()

and my Item

class ConcreteType(override val type: String = "") : Item {
    var something by mutableStateOf("beep")

then in my VM I call

(myItem as ConcreteType).something = "boop"

My composable always beeps, but never boops.

[KamilH]

When you change the underlaying var, you doesn’t actually mutate the list. Make your `ConcreteType`’s property not mutable and when you want your composable to recompose, replace the value on the list.

I think having MutableList of mutableStateOf can be called “2 degrees of mutability” that has been described by Zach in mentioned blog post

[Colton Idle]

Yeah, that did cross my mind with having a mutable state inside of a mutable list, but I only felt fine with it because Adam Powell (and others) kinda led me towards this path for another similar case where I had a mutable list of people, and each person had a mutable state of "isChecked". And so that use case seemed valid in that thread, and so I could only think that my use case here is valid? Prev thread: https://kotlinlang.slack.com/archives/CJLTWPH7S/p1637203859164500?thread_ts=1637187114.148800&cid=CJLTWPH7S

[KamilH]

In the previous example you did this:

vm.state.people.forEach {
    TextButton(onClick = {
    it.selected = true
})

so for each people you put TextButton, do you do the same in current example? Or maybe you put your items in the LazyColumn for example?

[Colton Idle]

Hm. You might be onto something there. In the current example I only do what you see above in the original question. I'm trying to edit directly.

What's intersting is that I don't actually technically need the original list to be a mutableStateListOf, so I switched over to

val list = mutableListOf<Item>()

and so that only leaves me with mutableState inside of the ConcreteType and it still does not work.

[Colton Idle]

Okay. Even went ahead and converted my list to

var list = listOf<Item>()

and it still Beeps. No boops.

[Colton Idle]

its like something about mutableStateOf in a polymorphic type isn't supported maybe?

[Colton Idle]

😭
It was user error. I had a rogue parent that had a remember function surrounding my actual composable. Things seem to be updating now. I'm going to revert and do a bunch of sanity checks to try out the two degrees of mutability thing.

[Colton Idle]

Every variation that we talked about above ended up working. no issues with the 2 degrees of mutability sort of thing. i assume because it wasn't exposing multiple ways to mutate the single list (mutable within a mutable) and this was moreso that I had a mutable list, with non mutable elements, that had mutable properties? either way. Thank you @KamilH for rubberducking.

[KamilH]

I’m glad you found where the problem is

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

It's fine to mutate objects' properties inside a list if those properties are backed by mutable state. I'm not sure how you even managed to get a composable inside a remember function, that shouldn't even compile 😅