Is there any problem with this sample? `var currentDessertImageId by rememberSaveable *{*` `_mut...

# compose

[Pablo]

Is there any problem with this sample?
var currentDessertImageId by rememberSaveable *{*
_mutableStateOf_(desserts[uiState.value.currentDessertIndex].imageId)
}
Something is not working because each recomposition, currentDessertImageId is not changing... is always the same, and that is not normal because each recomposition currentDessertIndex is different, and desserts[uiState.value.currentDessertIndex].imageId is different too, I checked it with a Log.

This is the Log:

2024-02-26 15:11:21.014  6790-6790  XXXX com.example.dessertclicker D  currentDessertIndex: 0 + desserts[uiState.value.currentDessertIndex].imageId: 2130968578 + currentDessertImageId: 2130968578
2024-02-26 15:11:23.098  6790-6790  XXXX com.example.dessertclicker D  currentDessertIndex: 1 + desserts[uiState.value.currentDessertIndex].imageId: 2130968579 + currentDessertImageId: 2130968578
2024-02-26 15:11:23.248  6790-6790  XXXX com.example.dessertclicker D  currentDessertIndex: 2 + desserts[uiState.value.currentDessertIndex].imageId: 2130968580 + currentDessertImageId: 2130968578

[Chrimaeon]

you’ll need to pass the currentDessertIndex as an input parameter to remeberSavable otherwise, as the name suggests, its “remembered”.

[Pablo]

@Chrimaeon can you explain it please? I don't know why passing currentDessertIndex should behave different than passing imageId

[Pablo]

both are integer values

[Pablo]

and both are changing each recomposition

[Chrimaeon]

val currentIndex = uiState.value.currentDessertIndex
    var currentDessertImageId by rememberSaveable(currentIndex) {
        mutableStateOf(desserts[currentIndex].imageId)
    }

without the “input” parameter the `remember`’s closure is only called once with the first value. remeberX does not know that you “input” has changed and need to re-evaluate.

[Chrimaeon]

also if desserts change over time, you’ll need to pass that as well.

[Chrimaeon]

https://developer.android.com/jetpack/compose/state#retrigger-remember

[Chrimaeon]

remember stores the value until it leaves the Composition. However, there is a way to invalidate the cached value. The remember API also takes a key or keys parameter. If any of these keys change, the next time the function recomposes, remember invalidates the cache and executes the calculation lambda block again. This mechanism gives you control over the lifetime of an object in the Composition. The calculation remains valid until the inputs change, instead of until the remembered value leaves the Composition.

[Pablo]

oh, I see, now I know where is the problem, I was killing flies with cannon shots 😄

[Pablo]

I can solve the isssue simply not using the remember, and just doing this:
val currentDessertImageId = desserts[uiState.value.currentDessertIndex].imageId

[Pablo]

I'm migrating a sample project to viewmodel and this is a huge mistake from me

[Pablo]

I noticed it thanks to you

[Pablo]

I don't need to remember a value that is changing in each recomposition!

[Pablo]

now those values are stored in a viewmodel, inside that UiState class

[Pablo]

now all it's clear, thanks

[Pablo]

my brain is still changing to using declarative uis, states, etc..