@Quawetim I don't know which is better. For my comprehension, it is easier to use implicitHeight/implicitWidth of the item to be scrolled.
For example, when the item is a ListView, implicitHeight is automatically updated when an element from the ListView is changed/added/removed.
Your View item only have to set implicitHeight/implicitWidth and dynamically the ListView will adapt the scollbars limits/positions