I want to use

value class

with

String

as

key

for

LazyColumn

item. Unfortunately I received

Type of the key testString is not supported. On Android you can only use types which can be stored inside the Bundle

Is there any chance to add custom

Saver

to

LazyColumn

or to add support for

value class

?

You can use

key = { index -> items[index].value },

Yes, I know but it's not obvious

what is not obvious?

Using

.value

getter for

value class

which should be transparent in many cases. But it's not in this case

I plugged this into a sample app of mine and it compiled fine

@JvmInline
value class Id(val value: String)

@Composable
private fun WeatherForecast(
    state: WeatherState,
    modifier: Modifier = Modifier,
) {
    LazyVerticalGrid(
        columns = GridCells.Adaptive(
            minSize = WeatherCardWidth,
        ),
        modifier = modifier,
        contentPadding = PaddingValues(all = MarginDouble),
        horizontalArrangement = Arrangement.spacedBy(MarginDouble),
        verticalArrangement = Arrangement.spacedBy(MarginDouble),
    ) {
        state.forecastItems.forEach { dayForecast ->
            item(
                key = Id(dayForecast.header.id),
                span = { GridItemSpan(maxLineSpan) }
            ) {
                ForecastHeader(
                    state = dayForecast.header,
                    modifier = Modifier
                        .fillMaxWidth()
                        .padding(vertical = MarginDouble),
                )
            }
            items(
                items = dayForecast.forecast,
                key = { hourForecast -> Id(hourForecast.id.toString()) }
            ) { hourForecast ->
                ForecastWeatherCard(
                    state = hourForecast,
                    modifier = Modifier.fillMaxWidth(),
                )
            }
        }
    }
}

if you are getting an error, you could try to make your value class parcelable with

@Parcelize