Uses WebControls to allow content to be written to multiple areas on the same view using ASP.NET MVC

MVC_ContentArea_ContentDisplayArea.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Web;
using System.Web.UI;

namespace MvcWebControls {

    /// <summary>
    /// Creates a zone that writes content to the matching ContentArea
    /// </summary>
    public class ContentArea : TemplateControl {

        #region Constants

        private const string CONTENT_AREA_CONTAINER = "AreaContainers";

        #endregion

        #region Constructors

        /// <summary>
        /// Creates a new ContentArea that allows you to write content to ContentDisplayAreas
        /// </summary>
        public ContentArea() {
            ContentArea._Areas.Add(this);
        }

        #endregion

        #region Properties

        /// <summary>
        /// The name of the content marker to write content to
        /// </summary>
        public string Target { get; set; }

        #endregion

        #region Shared Information

        //returns a list of content areas for the page
        internal static List<ContentArea> _Areas {
            get {

                //attempt to find the container and create a 
                //new one if it hasn't been found yet
                List<ContentArea> containers =
                    HttpContext.Current.Items[CONTENT_AREA_CONTAINER] as List<ContentArea>;
                if (containers == null) {
                    containers = new List<ContentArea>();
                    HttpContext.Current.Items[CONTENT_AREA_CONTAINER] = containers;
                }

                //return the generated container
                return containers;

            }
        }


        //gets the content for this control
        internal LiteralControl _GetContent() {

            //write the content to a string
            using (StringWriter output = new StringWriter()) {
                using (_ContentAreaWriter html = new _ContentAreaWriter(output)) {

                    //write the content
                    base.Render(html);

                    //create the content and return it as a control
                    string content = output.ToString();
                    return new LiteralControl(content);

                }
            }
        }

        #endregion  

        #region Handling Events

        //do not render these areas
        protected override void Render(HtmlTextWriter writer) {
            if (!(writer is _ContentAreaWriter)) { return; }
            base.Render(writer);

            //don't actually ever render this to
            //the real HTML writer
            //base.Render(writer);
        }

        #endregion

        #region Helper Classes

        private class _ContentAreaWriter : HtmlTextWriter {
            public _ContentAreaWriter(TextWriter writer) : base(writer) { }
        }

        #endregion

    }

    /// <summary>
    /// Consumes content written into markers
    /// </summary>
    [ParseChildren(true)]
    [PersistChildren(false)]
    public class ContentDisplayArea : Control {

        #region Properties

        /// <summary>
        /// Should this accepts any targets even if the case of
        /// the names do not match
        /// </summary>
        public bool IgnoreCase { get; set; }

        /// <summary>
        /// Ignores ContentAreas that have matching IDs
        /// </summary>
        public bool IgnoreDuplicates { get; set; }

        #endregion

        #region Constructors

        /// <summary>
        /// Creates a new area to write content to
        /// </summary>
        public ContentDisplayArea() {
        }

        #endregion

        #region Handling Events

        //handles finding the correct areas to render
        protected override void Render(HtmlTextWriter writer) {
            this.ID = this.ID ?? string.Empty;

            //get the correct way to handle case
            StringComparison compare = this.IgnoreCase 
                ? StringComparison.OrdinalIgnoreCase 
                : StringComparison.Ordinal;

            //get a list of IDs to track
            List<string> added = new List<string>();

            //add all of the controls that exist for this page
            foreach (ContentArea area in ContentArea._Areas) {
                if (!this.ID.Equals(area.Target, compare)) { continue; }

                //check the IDs for duplicates
                if (this.IgnoreDuplicates && 
                    !string.IsNullOrEmpty(area.ID) &&
                    added.Any(item => item.Equals(area.ID, compare))) {
                    continue;
                }

                //add the ID of the items checked
                if (area.ID is string) {
                    added.Add(area.ID ?? string.Empty);
                }

                //add each of the child controls
                this.Controls.Add(area._GetContent());

                //No need to hide controls since ContentAreas
                //aren't actually ever rendered
                //area.Controls.Clear();

            }

            //finally, render the control normally
            base.Render(writer);

        }

        #endregion

    }

}