private void Page_Loaded(object sender, RoutedEventArgs e)
        {
            customers = App._customers;

            if (customers == null)
            {
                customers = My_Storage.ReadXml <ObservableCollection <Customer> >("backup/Customers.xml");
                MessageBox.Show("Your Customer data file name has been edited , a backup copy was reloaded");
            }

            list_customers.ItemsSource = customers;
        }
        private void Page_Loaded(object sender, RoutedEventArgs e)
        {
            bikes = App._bikes;

            if (bikes == null)
            {
                bikes = My_Storage.ReadXml <ObservableCollection <Bike> >("backup/Bikes.xml");

                System.Windows.MessageBox.Show("Your Customer data file name has been edited , a backup copy was reloaded");
            }

            listBox_bikes.ItemsSource = bikes;
        }