How to select multiple items in LazyColumn in JetpackCompose

Question

How to select multiple items in LazyColumn and finally add the selected items in a seperate list.

               GettingTags(tagsContent ={ productTags ->

                val flattenList = productTags.flatMap {
                    it.tags_list
                }
                Log.i(TAG,"Getting the flattenList $flattenList")

                LazyColumn{
                    items(flattenList){
                        ListItem(text = {Text(it) })
                        if(selectedTagItem) {
                            Icon(
                                imageVector = Icons.Default.Check,
                                contentDescription = "Selected",
                                tint = Color.Green,
                                modifier = Modifier.size(20.dp)
                            )
                        }
                    }
                }

            })

Mutable variable state

var selectedTagItem by remember{
    mutableStateOf(false)
}

Answer 1

First create a class with selected variable to toggle

@Immutable
data class MyItem(val text: String, val isSelected: Boolean = false)

Then create a SnapshotStateList via mutableStateListOf that contains all of the items, and can trigger recomposition when we update any item with new instance, add or remove items also. I used a ViewModel but it's not mandatory. We can toggle items using index or get selected items by filtering isSelected flag

class MyViewModel : ViewModel() {

    val myItems = mutableStateListOf<MyItem>()
        .apply {
            repeat(15) {
                add(MyItem(text = "Item$it"))
            }
        }

    fun getSelectedItems() = myItems.filter { it.isSelected }

    fun toggleSelection(index: Int) {

        val item = myItems[index]
        val isSelected = item.isSelected

        if (isSelected) {
            myItems[index] = item.copy(isSelected = false)
        } else {
            myItems[index] = item.copy(isSelected = true)
        }
    }
}

Create LazyColumn with key, key makes sure that only updated items are recomposed, as can be seen in performance document

@Composable
private fun SelectableLazyListSample(myViewModel: MyViewModel) {

    val selectedItems = myViewModel.getSelectedItems().map { it.text }
    Text(text = "Selected items: $selectedItems")
    LazyColumn(
        verticalArrangement = Arrangement.spacedBy(8.dp),
        contentPadding = PaddingValues(8.dp)
    ) {
        itemsIndexed(
            myViewModel.myItems,
            key = { _, item: MyItem ->
                item.hashCode()
            }
        ) { index, item ->
            Box(
                modifier = Modifier
                    .fillMaxWidth()
                    .background(Color.Red, RoundedCornerShape(8.dp))
                    .clickable {
                        myViewModel.toggleSelection(index)
                    }
                    .padding(8.dp)
            ) {
                Text("Item $index", color = Color.White, fontSize = 20.sp)
                if (item.isSelected) {
                    Icon(
                        modifier = Modifier
                            .align(Alignment.CenterEnd)
                            .background(Color.White, CircleShape),
                        imageVector = Icons.Default.Check,
                        contentDescription = "Selected",
                        tint = Color.Green,
                    )
                }
            }
        }
    }
}

Result