AutoCatAvalonia/AutoCat/App.axaml.cs

using AutoCat.Utils;
using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Markup.Xaml;
using AutoCat.ViewModels;
using AutoCat.Windows;
using AutoCatCore.Services.Api;
using AutoCatCore.Services.Storage;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace AutoCat;

public partial class App : Application
{
    public IHost AppHost { get; private set; }

    private static void RegisterDependencies(HostBuilderContext context, IServiceCollection services)
    {
        // Services
        services.AddSingleton<IStorageService, StorageService>();
        services.AddSingleton<IApiService, ApiService>();
                
        // ViewModels
        services.AddTransient<HistoryViewModel>();
        services.AddTransient<AuthWindowViewModel>();
        services.AddTransient<MainWindowViewModel>();
                
        // Windows
        services.AddWindowFactory<AuthWindow>();
        services.AddWindowFactory<MainWindow>();
    }

    public App()
    {
        AppHost = Host.CreateDefaultBuilder()
            .ConfigureServices(RegisterDependencies)
            .Build();
    }

    public override void Initialize()
    {
        AvaloniaXamlLoader.Load(this);
    }

    public override void OnFrameworkInitializationCompleted()
    {
        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
        {
            var storageService = AppHost.Services.GetRequiredService<IStorageService>();

            desktop.MainWindow = storageService.IsLoggedIn
                ? AppHost.Services.GetRequiredService<MainWindow>()
                : AppHost.Services.GetRequiredService<AuthWindow>();
        }

        base.OnFrameworkInitializationCompleted();
    }
}