Modifying a SnapshotStateList throws ConcurrentModificationException-CodePudding

The documentation of SnapshotStateList states that it is similar to a regular mutable list. I have a use case where I need to modify all the elements in the list (set case). This does not change the size of the list, but I'm running into ConcurrentModificationException.

I have created a very simplified version of my usecase here. The following kotlin list works fine:

val myList2 = mutableListOf("a", "b", "c")
myList2.forEachIndexed { index, _ ->
    // Modify item at index
    myList2[index] = "x"
}

But I get a concurrent modification exception here:

val myList = mutableStateListOf("a", "b", "c")
myList.forEachIndexed { index, _ ->
    // Modify item at index but I get an exception
    myList[index] = "x"
}

How can I modify all elements of mutableStateList() in place without getting the concurrent modification exception?

Edit:

I can create a copy of the mutableStateList to iterate over which works fine but since I'm not changing the size of the list, is it possible to do it in place?

CodePudding user response：

Some possible workarounds are to use replaceAll to transform the list in-place (as long as you don't need the index), or just use an old-fashioned loop over indices if you do

val listA = mutableListOf("A","B","C")

// this works
listA.forEachIndexed { i, s ->
    listA[i] = s.lowercase()
}

val listB = mutableStateListOf("A","B","C")

// this fails - as you noted
listB.forEachIndexed { i, s ->
    listB[i] = s.lowercase()
}

// this works, as long as you don't need the index
listB.replaceAll { s -> s.lowercase() }

// this also works, and lets you have the index
for(i in listB.indices) {
    listB[i] = listB[i].lowercase()
}