private void deleteBookBtn_Click(object sender, EventArgs e) { if (lbBooks.SelectedItem == null) { MessageBox.Show("Please select a book you would like to delete."); } else if (bookService.BookHasBookCopies(lbBooks.SelectedItem as Book)) { MessageBox.Show("You have to remove all the bookcopies related to the book before you can delete the book."); } else { bookService.Remove(lbBooks.SelectedItem as Book); } }