Register services in the Microsoft.Extensions.DependencyInjection container

AppServices.cs

public class AppServices
{
    private AppServices()
    {
        var services = new ServiceCollection();

        // view-models
        services.AddTransient<BooksViewModel>();

        // services
        services.AddTransient<IItemsService<Book>, BooksService>();
        services.AddTransient<IShowProgressInfo, ShowProgressInfo>();

        // stateful services
        services.AddScoped<IItemToViewModelMap<Book, BookItemViewModel>, BookToBookItemViewModelMap>();
        services.AddScoped<ISharedItems<Book>, SharedItems<Book>>();
        services.AddScoped<IRepository<Book, int>, BooksSampleRepository>();

        // logging configuration
        services.AddLogging(builder =>
        {
#if DEBUG
            builder.AddDebug().SetMinimumLevel(LogLevel.Trace);
#endif
        });

        ServiceProvider = services.BuildServiceProvider();
    }

    public IServiceProvider ServiceProvider { get; }

    private static AppServices _instance;
    private static readonly object _instanceLock = new object();
    private static AppServices GetInstance()
    {
        lock (_instanceLock)
        {
            return _instance ?? (_instance = new AppServices());
        }
    }
    
    public static AppServices Instance => _instance ?? GetInstance();
}