using `Map` like: `mutableStateOf(map)` and reassigning that `Map` doesn’t trigger recomposition? h...

# compose

[Marko Novakovic]

using Map like: mutableStateOf(map) and reassigning that Map doesn’t trigger recomposition? how can I approach this?

[Teodor Penkov]

what kind of things do you store in the map?

[Marko Novakovic]

Map<enum class, Double>

[John O'Reilly]

this might be relevant https://dev.to/zachklipp/two-mutables-dont-make-a-right-2kgp

[Marko Novakovic]

thanks! I’ll take a look. didn’t know 6th part came out 🦜

[Teodor Penkov]

yea that’s really nice article, maybe you could try to figure it out with a flow

[John O'Reilly]

but I might be misunderstanding....when you say "reassigning that `Map`" do you mean updating values in the map or setting a new value to your mutableStateOf value?

[Marko Novakovic]

neither works

[Marko Novakovic]

article even says:

If someone sent you a link to this post as a reply to a question on Slack or somewhere, and you just want a quick answer, here you go:

Don't put mutable collections inside mutable state holders.

hahahaha

[eygraber]

I would think that the following should work:

var map by mutableStateOf(mutableMapOf(1 to 2))
map = mutableMapOf(2 to 1)

That doesn't cause recomposition?

[Marko Novakovic]

private val _map = mutableMapOf()
val map by mutableStateOf(map)
.....
_map[key] = value
map = HashMap(_map)

the gist of what am doing
it does’t trigger recomposition

[Marko Novakovic]

I tried just assigning it without HashMap just map = _map but that doesn’t work either
I introduced HashMap in hope that creating new object will work

[philglass]

You're doing exactly what the article above tells you not to, nested mutability with a MutableState<MutableMap<X, Y>>. The value you're assigning to map is equal to its current value (in this case "deep equal", not reference equal, but the effect is the same), so by design no change notifications are sent.

[Marko Novakovic]

today I’ll read the article, finally

[Marko Novakovic]

one thing tho, I used SideEffect and it actually triggers on every change so I added remember(state.map) { mutableStateOf(state.map) } and everything works