In my WPF application, I’m using a Frame for navigation between pages. The issue I’m encountering is that whenever I navigate to a page that is already open, a new instance of that page is added to the navigation history. This results in multiple instances of the same page being stored in the history, which I want to avoid.
This is what I want to avoid

The class that I use to navegate is this I tried to avoid it creating only one instance of the class but it dosn’t work for my problem:

using System.Windows;

    public partial class MainPage : Window
    {
        public ClientWindow ClientsPage;
        public InvoiceWindow DraftInvoicePage;
        public InvoiceWindow IssuedInvoicePage;
        public InvoiceWindow SentInvoicePage;

        public MainPage()
        {
            InitializeComponent();
            MainFrame.Navigate(new DefaultPage(this));
        }

        public void LoadClientsPage(object sender, RoutedEventArgs e)
        {
            if (ClientsPage == null)
            {
                ClientsPage = new ClientWindow();
            }
            MainFrame.Navigate(ClientsPage);
        }

        public void LoadDraftInvoicesPage(object sender, RoutedEventArgs e)
        {
            if (DraftInvoicePage == null)
            {
                DraftInvoicePage = new InvoiceWindow(InvoiceWindow.InvoiceType.Draft);
            }
            MainFrame.Navigate(DraftInvoicePage);
        }

        public void LoadIssuedInvoicesPage(object sender, RoutedEventArgs e)
        {
            if (IssuedInvoicePage == null)
            {
                IssuedInvoicePage = new InvoiceWindow(InvoiceWindow.InvoiceType.Issued);
            }
            MainFrame.Navigate(IssuedInvoicePage);
        }

        public void LoadSentInvoicesPage(object sender, RoutedEventArgs e)
        {
            if (SentInvoicePage == null)
            {
                SentInvoicePage = new InvoiceWindow(InvoiceWindow.InvoiceType.Sent);
            }
            MainFrame.Navigate(SentInvoicePage);
        }

        public void OpenConfiguration(object sender, RoutedEventArgs e)
        {
            ConfigurationWindow configWindow = new ConfigurationWindow();
            configWindow.ShowDialog();
        }
    }