Can't navigate windows

Describe the bug

I try to make a login page which users will users use username and password to see Mainwindow.xaml that generated by WPF UI Template. Here is my code ;

This is the Login.xaml.cs
` public partial class Login
{
private MainWindowViewModel viewModel;
private PageService pageService;
private NavigationService navigationService;
private readonly AuthenticationService _authService;

 public LoginViewModel ViewModel { get; }
 public Login()
 {
     InitializeComponent();
     _authService = new AuthenticationService(); // AuthenticationService örneği
 }



 private void LoginButton_Click(object sender, RoutedEventArgs e)
 {
     string username = UsernameText.Text; // Kullanıcı adı TextBox'ı
     string password = PasswordText.Password; // Şifre PasswordBox'ı

     if (_authService.Authenticate(username, password))
     {
         System.Windows.MessageBox.Show("Giriş başarılı!", "Bilgi", System.Windows.MessageBoxButton.OK, MessageBoxImage.Information);
         DialogResult = true; // Login başarılı -> Giriş ekranını kapat
         Close();
     }
     else
     {
         System.Windows.MessageBox.Show("Kullanıcı adı veya şifre hatalı.", "Hata", System.Windows.MessageBoxButton.OK, MessageBoxImage.Error);
     }
 }

}`

That's the AuthenticationService.cs

`public class AuthenticationService
{
private readonly Dictionary<string, string> _users;

public AuthenticationService()
{
    // Örnek kullanıcılar: Kullanıcı adı ve şifre çiftleri
    _users = new Dictionary<string, string>
    {
        { "admin", "12345" }, // Kullanıcı adı: admin, Şifre: 12345
        { "user1", "password" }
    };
}

/// <summary>
/// Kullanıcı adı ve şifre doğrulaması yapar.
/// </summary>
/// <param name="username">Kullanıcı adı</param>
/// <param name="password">Şifre</param>
/// <returns>Doğrulama sonucu (true/false)</returns>
public bool Authenticate(string username, string password)
{
    return _users.TryGetValue(username, out var storedPassword) && storedPassword == password;
}

}`

ApplicationHostService ;

` private async Task HandleActivationAsync()
{
// Login.xaml'i başlangıç ekranı olarak göster
if (!Application.Current.Windows.OfType().Any())
{
var loginWindow = new Login();
bool? loginResult = loginWindow.ShowDialog(); // Giriş ekranını modal olarak göster

     if (loginResult != true || !UserIsAuthenticated())
     {
         // Kullanıcı giriş yapmadıysa uygulamayı kapat
         Application.Current.Shutdown();
         return;
     }
 }

 // Kullanıcı doğrulandıysa MainWindow'u başlat
 if (!Application.Current.Windows.OfType<MainWindow>().Any())
 {
     _navigationWindow = (
         _serviceProvider.GetService(typeof(INavigationWindow)) as INavigationWindow
     )!;
     _navigationWindow!.ShowWindow();

     _navigationWindow.Navigate(typeof(Premium.Views.Pages.DashboardPage));
 }

 await Task.CompletedTask;

}`

To Reproduce

...

Expected behavior

If user credentials are true I want to switch to mainwindow

Screenshots

OS version

Windows 10

.NET version

.NET 8.0

WPF-UI NuGet version

3.0.5

Additional context

No response

Start with Login.xaml.cs, AuthenticationService.cs, and ApplicationHostService.HandleActivationAsync. Read how ShowDialog, ShowWindow, and the authentication check interact, then reproduce the login flow on Windows 10 with .NET 8 and WPF UI 3.0.5. Done means valid credentials reliably lead to the main window without prematurely shutting down the application.