asp.net UserControl

    [ParseChildren(true), PersistChildren(true)]
    public class IfDiv : UserControl
    {
        [TemplateContainer(typeof(UserControl))]
        public ITemplate Format { get; set; }

        [PersistenceMode(PersistenceMode.InnerProperty)]
        public List<Item> Items { get; set; }

        //Constructor
        public IfDiv()
        {
            Items = new List<Item>();
            Format = new StringITemplate(String.Empty);
        }

        //Methods
        protected override void Render(HtmlTextWriter writer)
        {
            string output;

            if (!Items.Any() || Items.Any(x => String.IsNullOrWhiteSpace(ParseITemplate(x.Text)))) output = String.Empty;
            else
            {
                var formatParams = Items.Select(x => ParseITemplate(x.Text)).Cast<object>().ToArray();
                output = String.Format(ParseITemplate(Format), formatParams);
            }

            writer.Write(output);
        }

        private static string ParseITemplate(ITemplate iTemplate)
        {
            //Return an empty string when the ITemplate is null
            if (iTemplate == null) return String.Empty;

            //Instantiate the template
            var container = new UserControl();
            iTemplate.InstantiateIn(container);
            var stringWriter = new StringWriter();
            container.RenderControl(new HtmlTextWriter(stringWriter));

            //Return
            var output = stringWriter.ToString();
            return output;
        }
    }

    public class StringITemplate : ITemplate
    {
        public string Template { get; set; }

        public StringITemplate(string template)
        {
            Template = template;
        }

        public void InstantiateIn(Control container)
        {
            var page = HttpContext.Current.Handler as Page;
            var tempContainer = page.ParseControl(Template);
            container.Controls.Add(tempContainer);
        }
    }

    [ParseChildren(true)]
    public class Item
    {
        //Properties
        [PersistenceMode(PersistenceMode.InnerDefaultProperty)]
        [TemplateContainer(typeof(UserControl))]
        public ITemplate Text { get; set; }

        //Constructors
        public Item() { }

        public Item(string text)
        {
            Text = new StringITemplate(text);
        }
    }