demo.cs

using System.Web.Mvc;
using Umbraco.Core;
using Umbraco.Core.Composing;
using Umbraco.Core.Models.PublishedContent;
using Umbraco.Web.Models;
using Umbraco.Web.Mvc;

namespace UmbracoDI
{
    public class MyComposer : IComposer
    {
        public void Compose(Composition composition)
        {
            composition.Register<IMyService, MyService>();
        }
    }

    public interface IMyService
    {
        string GetName();
    }

    public class MyService : IMyService
    {
        public string GetName() => "Morten";
    }

    public class ContentPageController : RenderMvcController
    {
        private readonly IMyService _myService;

        public ContentPageController(IMyService myService)
        {
            _myService = myService;
        }

        public ActionResult ContentPage(ContentModel model)
        {
            var vm = new ContentPageViewModel(model.Content)
            {
                SomeServiceName = _myService.GetName()
            };

            return CurrentTemplate(vm);
        }
    }

    public class ContentPageViewModel : ContentModel
    {
        public ContentPageViewModel(IPublishedContent content) : base(content) { }

        public string SomeServiceName { get; set; }
    }
}