private void btnOK_Click(object sender, RoutedEventArgs e)
{
string CustID = txtBoxCustomerID.Text;
int CID = Convert.ToInt32(CustID);
string name = txtBoxName.Text;
string address = txtBoxAddress.Text;
string phone = txtBoxPhone.Text;
controller.ChangeCustomer(CID, name, address, phone);
this.Close();
}