I have a list of data classes that I am displaying...

# compose

[Arpit Shukla]

I have a list of data classes that I am displaying using a LazyColumn. But even when a single item in the list changes, all the items inside LazyColumn are recomposed. I thought marking the data class as @Immutable might fix the issue but it didn't. How can I prevent these unnecessary recompositions? Code in 🧵

[Arpit Shukla]

@Immutable
data class EqualSplit(
    val name: String,
    val image: String,
    val number: String,
    val selected: Boolean
)

// In View Model
val equalSplits = mutableStateListOf<EqualSplit>()

fun onSplitSelectionChange(index: Int) {
    equalSplits[index] = equalSplits[index].let { it.copy(selected = !it.selected) }
}

LazyColumn {
    itemsIndexed(viewModel.equalSplits)  { index, split ->
        EqualSplitRowItem(
            split = split,
            onSelectionChange = { viewModel.onSplitSelectionChange(index) }
        )
    }
}

@Composable
private fun EqualSplitRowItem(
    split: EqualSplit,
    onSelectionChange: () -> Unit,
    modifier: Modifier = Modifier
) {
    Log.d("TAG", split.name) // This is printed for all items when any of the items change
    Row(
        modifier = modifier
            .clickable(onClick = onSelectionChange)
    ) {
        ...
    }
}

[Jon Boekenoogen]

You need to provide an implementation for the key function on itemsIndexed

[Arpit Shukla]

I updated my itemsIndexed to this:

itemsIndexed(
    items = viewModel.equalSplits,
    key = { _, split -> split.number }
) { index, split ->
    EqualSplitRowItem(
        split = split,
        onSelectionChange = { viewModel.onSplitSelectionChange(index) }
    )
}

It didn't work :(
@Adam Powell Does it have to do something with the onSelectionChange lambda? Is it possible that Compose doubts the lambda might have changed and so it always recomposes everything??