I am trying to learn Umbraco, so I am very new to it. I am sure, that there is a simple answer for my question.

I try to fill up a dropdown box in a content edit form with values, as the user have defined in a Document Type Collection in the context menu (not sure if I am using the right terms here)

Just for understanding of my task, the user of the site, can create their own business categories, that should be visible in a dropdown box. So when the user wants to define a company, the user can choose between different business types for the company.

I have defined a IUserComponent and a IComponent to inject Umbraco when it starts up, and that is working just fine. But when I am going to read the values from the collections, I can not find out, how to read the collection list.

public class InitDropDownComponent : IComponent { private readonly IContentService _contentService; private readonly IContentTypeService _contentTypeService; private readonly ServiceContext _serviceContext;

    public void Initialize()
    {
        BusinessCategories();
    }

    public void Terminate()
    {
    }


    public InitDropDownComponent(IContentService contentService, IContentTypeService contentTypeService, ServiceContext serviceContext)
    {
        _contentService = contentService;
        _contentTypeService = contentTypeService;
        _serviceContext = serviceContext;
    }

    public void BusinessCategories()
    {
        var businessCategoriesContent = _contentTypeService.Get(Guid.Parse("3d988d58-609c-452c-bb37-e600564751ba"));
        IEnumerable<IContentType> contentTypes = _contentTypeService.GetAll();
        IEnumerable<IContentType> contentTypes2 = _contentTypeService.GetChildren(Guid.Parse("3d988d58-609c-452c-bb37-e600564751ba"));
        var contentTypes3 = _contentTypeService.GetChildren(1378);
            EntityContainer container = _contentTypeService.GetContainer(1378);
        var fff = _contentTypeService.GetAllElementTypes();
        var content = _contentTypeService.Get(Guid.Parse("3d988d58-609c-452c-bb37-e600564751ba")) as IPublishedContent;
        var content2 = _serviceContext.ContentService.GetById(1378) as IPublishedContent; 
}

I got confused when to use IContentService, IContentTypeService and the ServiceContext or is it the right interfaces for this.

And may be there is a smarter way of doing a task like this, I don't know. Hope someone can bring me in the right direction