I want to use `value class` with `String` as `key` for `LazyColumn` item. Unfortunately I received &...

# compose

[Wojciech Rozwadowski]

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?

[Wojciech Rozwadowski]

@JvmInline
value class Id(val value: String)

val items = listOf(Id("testString"), Id("123"))
LazyColumn {
    items(
        items = items,
        key = { index -> items[index] }, // `items[index].value` is not obvious imho
    ) { index ->
        Text(items[index].value)
    }
}

[Francesc]

You can use

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

[Wojciech Rozwadowski]

Yes, I know but it's not obvious

[Francesc]

what is not obvious?

[Wojciech Rozwadowski]

Using .value getter for value class which should be transparent in many cases. But it's not in this case

[Francesc]

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