@Override
    public Parcelable onSaveInstanceState() {
        if (pendingSavedState != null) {
            return pendingSavedState;
        }

        // Check if we're detached; if not, update
        if (adapter != null)
            updateFirstAdapterPosition();
        SavedState state = new SavedState();
        state.firstViewAdapterPosition = firstViewAdapterPosition;
        state.firstViewTop = firstViewTop;

        return state;
    }
Assign callback object to be notified when a header view position changes between states of the HeaderPosition enum

@param headerPositionChangedCallback the callback
@see HeaderPosition
android/modules/module_common/src/main/java/github/tornaco/android/thanos/widget/section/StickyHeaderLayoutManager.java