@Override
            public void onInvalidated() {
                cancel();
            }
Caches DragSortItemView child heights. Sometimes DSLV has to
know the height of an offscreen item. Since ListView virtualizes
these, DSLV must get the item from the ListAdapter to obtain
its height. That process can be expensive, but often the same
offscreen item will be requested many times in a row. Once an
offscreen item height is calculated, we cache it in this guy.
Actually, we cache the height of the child of the
DragSortItemView since the item height changes often during a
drag-sort.
third_party/DragSortListView/src/com/mobeta/android/dslv/DragSortListView.java