private void SaveChanges(object sender, EventArgs e)
        {
            if (authorsListBox.SelectedIndex == -1 || publishersListBox.SelectedIndex == -1 || genresListBox.SelectedIndex == -1)
            {
                MessageBox.Show("Pogreska pri unosu. Sva polja moraju imati sadrzaj!", "Error", MessageBoxButtons.OK,
                                MessageBoxIcon.Error);
            }
            else
            {
                var title         = bookTitleTextBox.Text;
                var author        = authorsListBox.SelectedItem.ToString();
                var publisher     = publishersListBox.SelectedItem.ToString();
                var genre         = genresListBox.SelectedItem.ToString();
                var numberOfPages = numberOfPagesTextBox.Text;
                var totalBooks    = totalBooksTextBox.Text;

                var isSaved = _booksRepository.AddOrEditBook(title, author, publisher, genre, numberOfPages, totalBooks, null);

                if (!isSaved)
                {
                    MessageBox.Show("Pogreska pri unosu. Sva polja moraju imati sadrzaj!", "Error", MessageBoxButtons.OK,
                                    MessageBoxIcon.Error);
                }
                else
                {
                    MessageBox.Show("Knjiga uspjesno spremljena!", "Message", MessageBoxButtons.OK,
                                    MessageBoxIcon.Information);
                    Close();
                }
            }
        }