private void btnChange_Click(object sender, RoutedEventArgs e)
{
string ISBN = txtBoxBookISBN.Text;
string title = txtBoxTitle.Text;
string publisher = txtBoxPublisher.Text;
string author = txtBoxAuthor.Text;
string numberofpages = txtBoxNrOfPages.Text;
int nrpages = Convert.ToInt32(numberofpages);
string printyear = txtBoxYearPrinted.Text;
int pyear = Convert.ToInt32(printyear);
controller.ChangeBook(ISBN, title, nrpages, pyear, publisher, author);
this.Close();
}