TemplateComponent.cs

using System.Linq;
using Umbraco.Core.Composing;
using Umbraco.Core.Events;
using Umbraco.Core.Models;
using Umbraco.Core.Persistence.Repositories;
using Umbraco.Core.Services;
using Umbraco.Core.Services.Implement;

namespace Adventure.Core
{
    public class TemplateComposer : ComponentComposer<TemplateComponent> { }

    public class TemplateComponent : IComponent
    {
        private readonly ITemplateRepository _templateRepository;

        public TemplateComponent(ITemplateRepository templateRepository)
        {
            _templateRepository = templateRepository;
        }

        public void Initialize()
        {
            ContentTypeService.Saving += ContentTypeService_Saving;
        }

        private void ContentTypeService_Saving(IContentTypeService sender, SaveEventArgs<IContentType> e)
        {
            var template = _templateRepository.Get("superDuperMasterTemplate");
            if (template == null) return;

            foreach (var entity in e.SavedEntities.Where(x => x.HasIdentity == false))
            {
                entity.SetDefaultTemplate(template);
            }
        }

        public void Terminate() { }
    }
}