MyScreen.kt

// [...] Composable screen code 
when (state) {
    MainState.Loading -> {
        ItemCard(
            item = fakeData,
            isLoading = true,
        )
    }

    is MainState.Success -> {
        ItemCard(
            item = state.itemData,
            isLoading = false,
        )
    }
}

// Fake data to be used while loading and in the preview
private val fakeData = ItemData(
    imageResId = android.R.drawable.ic_dialog_info,
    title = LoremIpsum(4).values.toList().first(),
    description = LoremIpsum(8).values.toList().first(),
)

@PreviewLightDark
@Composable
fun ItemDataPreview() {
    ExampleTheme {
        ItemCard(item = fakeData)
    }
}