How to completely resort RecyclerView's SortedList

Question

The RecyclerView library recently added the new SortedList class. Suppose I have a callback that implements a compare() method that can change over time, i.e. the underlying Comparator can be switched out. What's the best way to tell the SortedList to completely resort its data?

Answer 1

Here's my own take on it (written in Kotlin):

list.beginBatchedUpdates()

val indices = (0..list.size() - 1).toArrayList()

while (!indices.isEmpty()) {
    val i = indices.first()
    val item = list.get(i)

    list.recalculatePositionOfItemAt(i)

    [suppress("USELESS_CAST_STATIC_ASSERT_IS_FINE")]
    indices.remove(list.indexOf(item) as Any) //cast to disambiguate remove()
}

list.endBatchedUpdates()

As you can see, I'm tracking the new index after every call to recalculatePositionOfItemAt() so every item is resorted only once and no item is skipped.

This works but seems really wasteful because recalculatePositionOfItemAt() will resize the underlying array twice to remove and then readd the item. indexOf will then perform a new binary search even though the index is already known.

Edit: This seems to lead to an infinite loop if items compare as equal.

Alternative approach (remove all, then add all):

list.beginBatchedUpdates()

val copy = (list.size() - 1 downTo 0).map { list.removeItemAt(it) }
copy.forEach { list.add(it) }

list.endBatchedUpdates()