private void btnEditCustomer_Click(object sender, RoutedEventArgs e)
 {
     if (CustomersGrid.SelectedIndex >= 0)
     {
         currentCustomer = CustomersGrid.SelectedItem as Customer;
         AddEditCustomer addWindow = new AddEditCustomer(customerDataAccess, currentCustomer);
         addWindow.ShowDialog();
     }
 }
        private void btnAddCustomer_Click(object sender, RoutedEventArgs e)
        {
            AddEditCustomer addWindow = new AddEditCustomer(customerDataAccess);

            addWindow.ShowDialog();
        }