Sitecore shared placeholders

GetFromLayoutFieldWithSharedPlaceholders.cs

using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
using Sitecore;
using Sitecore.Data;
using Sitecore.Data.Fields;
using Sitecore.Data.Items;
using Sitecore.Diagnostics;
using Sitecore.Mvc.Extensions;
using Sitecore.Mvc.Pipelines.Response.GetXmlBasedLayoutDefinition;
using Sitecore.Mvc.Presentation;

namespace Library.DotNet.Sc.Pipelines.GetXmlBasedLayoutDefinition
{
    public class GetFromLayoutFieldWithSharedPlaceholders : GetFromLayoutField
    {
        private readonly List<string> _placeholders = new List<string>();

        public void AddPlaceholder(string placeholders)
        {
            if (!string.IsNullOrEmpty(placeholders))
            {
                _placeholders.Add(placeholders);
            }
        }

        public string HomeItemTemplateId { get; set; }

        public override void Process(GetXmlBasedLayoutDefinitionArgs args)
        {
            if (args.Result == null)
            {
                XElement content = GetFromField(args);
                if (content != null)
                {
                    Item item = PageContext.Current.Item;
                    if (item != null && item.TemplateID != new ID(HomeItemTemplateId))
                    {
                        Log.Debug("GetFromLayoutField - Process : Not on homepage");
                        Item homeItem = Context.Database.GetItem(Context.Site.StartPath);
                        if (homeItem != null)
                        {
                            Field homePageLayoutField = homeItem.Fields[FieldIDs.LayoutField];
                            if (homePageLayoutField != null)
                            {
                                string fieldValue = LayoutField.GetFieldValue(homePageLayoutField);
                                if (!fieldValue.IsWhiteSpaceOrNull())
                                {
                                    XElement homePageLayout = XDocument.Parse(fieldValue).Root;
                                    XElement dXElement = content.Element("d");
                                    if (dXElement != null && homePageLayout != null)
                                    {
                                        XElement dXElementInHomePageLayout = homePageLayout.Element("d");
                                        if (dXElementInHomePageLayout != null)
                                        {
                                            var layoutElements = dXElementInHomePageLayout.Elements().ToList();

                                            foreach (var placeholder in _placeholders)
                                            {
                                                dXElement.Add(ExtractContentsFromLayout(layoutElements, placeholder));
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }

                args.Result = content;
            }
        }
        
        private List<XElement> ExtractContentsFromLayout(IEnumerable<XElement> layoutElements, string placeholder)
        {
            Log.Debug(string.Format("GetFromLayoutField - Process : Starting to extract for placeholder {0}:", placeholder));

            List<XElement> elements = new List<XElement>();

            if (layoutElements.Any())
            {
                foreach (XElement element in layoutElements)
                {
                    if (element.HasAttributes)
                    {
                        if (element.Attribute("ph") != null)
                        {
                            string value = element.Attribute("ph").Value.ToLowerInvariant();
                            if (!string.IsNullOrEmpty(value) && (value.StartsWith("/" + placeholder.ToLowerInvariant()) || value.Equals(placeholder.ToLowerInvariant())))
                            {
                                elements.Add(element);
                            }
                        }
                    }
                }
            }
            Log.Debug("GetFromLayoutField - Process : Done with extract");

            return elements;
        }
    }
}

Library.config

<?xml version="1.0" encoding="utf-8"?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <pipelines>
      <getPlaceholderRenderings>
        <processor type="Library.DotNet.Sc.Pipelines.GetPlaceholderRenderings.RemoveSharedRenderings, Library.DotNet.Sitecore"
                   patch:after="processor[@type='Sitecore.Pipelines.GetPlaceholderRenderings.RemoveNonEditableRenderings, Sitecore.Kernel']">
          <HomeItemTemplateId>{00000000-0000-0000-0000-000000000000}</HomeItemTemplateId>
          <Placeholders hint="list:AddPlaceholder">
            <string>site-header</string>
            <string>site-footer</string>
          </Placeholders>
        </processor>
      </getPlaceholderRenderings>
      <mvc.getXmlBasedLayoutDefinition>
        <processor type="Library.DotNet.Sc.Pipelines.GetXmlBasedLayoutDefinition.GetFromLayoutFieldWithSharedPlaceholders, Library.DotNet.Sitecore"
                   patch:instead="processor[@type='Sitecore.Mvc.Pipelines.Response.GetXmlBasedLayoutDefinition.GetFromLayoutField, Sitecore.Mvc']" >
          <HomeItemTemplateId>{00000000-0000-0000-0000-000000000000}</HomeItemTemplateId>
          <Placeholders hint="list:AddPlaceholder">
            <string>site-header</string>
            <string>site-footer</string>
          </Placeholders>
        </processor>
      </mvc.getXmlBasedLayoutDefinition>
    </pipelines>
  </sitecore>
</configuration>

RemoveSharedRenderings.cs

using System.Collections.Generic;
using Sitecore;
using Sitecore.Data;
using Sitecore.Data.Items;
using Sitecore.Diagnostics;
using Sitecore.Pipelines.GetPlaceholderRenderings;

namespace Library.DotNet.Sc.Pipelines.GetPlaceholderRenderings
{
    public class RemoveSharedRenderings
    {
        private readonly List<string> _placeholders = new List<string>();

        public void AddPlaceholder(string placeholders)
        {
            if (!string.IsNullOrEmpty(placeholders))
            {
                _placeholders.Add(placeholders);
            }
        }

        public string HomeItemTemplateId { get; set; }

        public void Process(GetPlaceholderRenderingsArgs args)
        {
            Assert.IsNotNull(args, "args");

            Item item = Context.Item;
            if (item != null && item.TemplateID != new ID(HomeItemTemplateId))
            {
                foreach (var placeholder in _placeholders)
                {
                    string value = args.PlaceholderKey;
                    if (!string.IsNullOrEmpty(value) && (value.StartsWith("/" + placeholder.ToLowerInvariant()) || value.Equals(placeholder.ToLowerInvariant())))
                    {
                        args.HasPlaceholderSettings = false;
                        args.PlaceholderRenderings.Clear();
                    }
                }
            }
        }
    }
}