Proper way to operate collections in StateFlow

Question

I'm creating MutableStateFlow like this:

val intSet = MutableStateFlow(HashSet<Int>())

And in some moment later I want to update collection in this flow:

intSet.value.add(0)

And this doesn't seem to work (the collection updates, but observers are not notified). The way that I found it working:

val list = HashSet<Int>(intSet.value)
list.add(0)
intSet.value = list

But it creates copy of the collection, so it doesn't look proper for me. Is there any simpler way to update collection in StateFlow?

Answer 1

MutableFlow does not check for changes in the content of collections. Only when the collection reference has changed it will emit the change.

Use immutable Set and use the += operator to add new elements. This will basically, create new Set and will trigger the change.

val intSetFlow = MutableStateFlow(setOf<Int>())
intSetFlow.value += 0