What is the VerticalScrollExtent in Android ScrollView?

It's kinda late, but hope it's ok.

1) The method actually is implemented by the subclasses. For example, this is what it looks like for AbsListView (ListView's superclass).
2) View's height can be different from its vertical scroll's height - just imagine a View with weird top/bottom padding .

These two points pretty much make other questions irrelevant :)

• compute*ScrollOffset - Defines the distance between the start of the scrollable area and the top of the current view window inside the scrollable area. So for example, if your list has 10 items and you've scrolled down so the 3rd item is at the top-most visible item, then the offset is 3 (or 3*itemHeight, see below).

• compute*ScrollExtent - Defines the size of the current view window inside the scrollable area. So for example, if your list has 10 items and you can currently see 5 of those items, then the extent is 5 (or 5*itemHeight, see below).

• compute*ScrollRange - Defines the size of the current scrollable area. So for example, if your list has 10 items then the range is 10 (or 10*itemHeight, see below).

Note that all these methods can return values in different units depending on their implementation, so for the examples above, I am using the indices, but in some cases these methods will return pixel values equivalent to the width or height of the items.

In particular, the LinearLayoutManager of the RecyclerView will return indices if the 'smooth scrollbar' feature is disabled, otherwise it will return pixel values. See ScrollbarHelper in the support library for more information.

Additional reading: https://groups.google.com/forum/#!topic/android-developers/Hxe-bjtQVvk