void MoveDown()
        {
            int itemIndex = AllBooks.IndexOf(SelectedBook);

            AllBooks.Move(itemIndex + 1, itemIndex);
            SelectedBook.BookID++;
            AllBooks[itemIndex].BookID--;
        }
        void MoveUp()
        {
            int itemIndex = AllBooks.IndexOf(SelectedBook);

            AllBooks.Move(itemIndex - 1, itemIndex);
            SelectedBook.BookID--;
            AllBooks[itemIndex].BookID++;
        }