//edit the chosen customer
        private void btn_editcustomer_Click(object sender, RoutedEventArgs e)
        {
            dynamic selected = lv_Customers.SelectedItem;

            //if no customer chosen then display error message
            if (selected == null)
            {
                MessageBox.Show("You haven't selected a customer to edit.");
                return;
            }
            int custRef = 0;

            custRef = selected.CustomerRef;
            Customer customer  = customerlist.Find(x => x.CustomerRef == custRef);
            var      newWindow = new CustomerWindow(this, customer);

            newWindow.ShowDialog();
        }
        //When the add customer button is pressed open an add customer window and pass through the mainwindow
        private void btn_addcustomer_Click(object sender, RoutedEventArgs e)
        {
            var newWindow = new CustomerWindow(this);

            newWindow.ShowDialog();
        }