`savedInstanceState` doesn't work in a NavHost. T...

# compose

[manueldidonna]

savedInstanceState doesn't work in a NavHost. This sample will always print '1'. Am I doing something wrong?

NavHost(navController, startDestination = "search") {
    composable("search") {
        var counter by savedInstanceState { 0 }
        counter += 1
        Log.d("counter", counter.toString())
    }
}

[Ian Lake]

I suspect you're actually looking for rememberSavedInstanceState if you want the state to be remembered across compositions

[manueldidonna]

@Ian Lake savedInstanceState should be rememberSavedInstanceState { mutableStateOf(init()) } . In fact my sample works if used in the Activity.setContent block

[manueldidonna]

From compose source code

@Composable
fun <T> savedInstanceState(
    vararg inputs: Any?,
    saver: Saver<T, out Any> = autoSaver(),
    key: String? = null,
    policy: SnapshotMutationPolicy<T> = structuralEqualityPolicy(),
    init: () -> T
): MutableState<T> = rememberSavedInstanceState(
    *inputs,
    saver = mutableStateSaver(saver, policy),
    key = key,
    init = { mutableStateOf(init(), policy) }
)

[Ian Lake]

So mutableStateOf works, but savedInstanceState isn't working for you? Do you mind filing a bug with a sample project? https://issuetracker.google.com/issues/new?component=409828

[Hitanshu Dhawan]

Hey, even I’m facing a similar issue like this.
I want to change the theme between light and dark on a click, for that I’m using savedInstanceState to store the current theme and change it.
The issue is calling setLightTheme(!isLightTheme) will change the theme, but after that isLightTheme is not changed to false and the theme is not changed.
Is this a bug? or am I doing something wrong?

setContent {
    val (isLightTheme, setLightTheme) = savedInstanceState { true }
    MyProjectTheme(lightTheme = isLightTheme) {
        val navController = rememberNavController()
        NavHost(navController, startDestination = "home") {
            composable("home") {
                HomeScreen(
                    onClick = { setLightTheme(!isLightTheme) }
                )
            }
        }

    }
}

[Hitanshu Dhawan]

@manueldidonna were you able to solve this issue or find a workaround?

[manueldidonna]

Nope, I haven't solved that issue. I'll file an issue in the tracker in the next hours

[manueldidonna]

Done @Ian Lake

[Hitanshu Dhawan]

Hey, is this issue fixed now in alpha-08 ?

[Hitanshu Dhawan]

Hi guys, wanted to know about this issue and the solution.

I have gone through these issues
• https://issuetracker.google.com/issues/174158395
• https://issuetracker.google.com/issues/173647680
• https://issuetracker.google.com/issues/172263305
The first and second are duplicates and last one is fixed, but still I’m facing this issue.

I have tried on compose version 1.0.0-alpha10 and navigation version 1.0.0-alpha05

My use case:
I want to toggle dark and light mode and I’m storing it as a state.

setContent {

            val (isLightTheme, setLightTheme) = remember { mutableStateOf(true) }

            McComposeTheme(lightTheme = isLightTheme) {
                HomeScreen {
                    setLightTheme(!isLightTheme)
                }
            }
        }

But this doesn’t seem to work.

Any help here please?

[Hitanshu Dhawan]

@Adam Powell