Hi there umbracos I am trying to figure out how to register a simple singleton service in the program.cs, but I am a bit lost, since there is a builder, but no services.

How is it supposed to be done? What is the .AddNotificationHandler doing in this context? I have done this, but it gives an error:

using Umbraco.Cms.Core.DependencyInjection;
using Microsoft.Extensions.DependencyInjection;


WebApplicationBuilder builder = WebApplication.CreateBuilder(args);


builder.CreateUmbracoBuilder()
    .AddBackOffice()
    .AddWebsite()
    .AddDeliveryApi()
    .AddComposers()
    .Services.AddSingleton<IDataService, DataService>()
    .Build();


WebApplication app = builder.Build();

The docs says: "

Registering dependencies for your site

When working with your site, and not a package, the recommended way to register dependencies is with the Program.cs file:

builder.CreateUmbracoBuilder()
    .AddBackOffice()
    .AddWebsite()
    .AddDeliveryApi()
    .AddComposers()
    // If you need to add something Umbraco specific, do it in the "AddUmbraco" builder chain, using the IUmbracoBuilder extension methods.
    .AddNotificationHandler<ContentTypeSavedNotification, ContentTypeSavedHandler>()
    .Build();"