updateItemAt
Updates the item at the given index and calls onChanged and/or onMoved if necessary.
You can use this method if you need to change an existing Item such that its position in the list may change.
If the new object is a different object (get(index) != item) and areContentsTheSame returns true, SortedList avoids calling onChanged otherwise it calls onChanged.
If the new position of the item is different than the provided index, SortedList calls onMoved.
Parameters
index
The index of the item to replace
item
The item to replace the item at the given Index.