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Sitecore provides a General link as an out-of-the-box field. This field enables Content Editors to insert links for one of the following options:

A. A link to the Sitecore item
B. Link to an external URL
C. A custom anchor tag
D. Email address
E. A JavaScript function
F. A Media link

Why this Blog?

At times, customers want to capture some additional information like google analytics tags, etc. Let’s look at how to add this additional field

In the Core DB, go to the external link item by tracking the path /Sitecore/system/Field Types/Link Types/ General Link/Menu/External Link and perform the below changes:

2. Write custom code to create a new message handler

A. Create custom control: Create a new class named ExternalLinkExtendForm, which will be inherited from the class ExternalLinkForm. The code for the same is presented in the shown image:

using Sitecore;
using Sitecore.DependencyInjection;
using Sitecore.Diagnostics;
using Sitecore.Shell.Applications.Dialogs.ExternalLink;
using Sitecore.Web.UI.HtmlControls;
using Sitecore.Web.UI.Sheer;
using Sitecore.Xml;
using System;
using System.Collections.Specialized;
using System.Xml;

namespace Foundation.Universal.Extensions
{
    public class ExternalLinkExtendForm: ExternalLinkForm
    {
        protected Edit FeatureName;
        protected Edit FeaturePosition;
        protected Edit FeatureOption;
        private ILinkExtendForm _linkExtendForm;
        public ExternalLinkExtendForm()
        {
            _linkExtendForm = (ILinkExtendForm)ServiceLocator.ServiceProvider.GetService(typeof(ILinkExtendForm));
            
        }

        private NameValueCollection customLinkAttributes;
        protected NameValueCollection CustomLinkAttributes
        {
            get
            {
                if (customLinkAttributes == null)
                {
                    customLinkAttributes = new NameValueCollection();
                    ParseLinkAttributes(GetLink());
                }

                return customLinkAttributes;
            }
        }

        protected override void ParseLink(string link)
        {
            base.ParseLink(link);
            ParseLinkAttributes(link);
        }

        protected virtual void ParseLinkAttributes(string link)
        {
            Assert.ArgumentNotNull(link, "link");
            XmlDocument xmlDocument = XmlUtil.LoadXml(link);
            if (xmlDocument == null)
            {
                return;
            }

            XmlNode node = xmlDocument.SelectSingleNode("/link");
            if (node == null)
            {
                return;
            }

            CustomLinkAttributes["FeatureNameAttributeName"] = XmlUtil.GetAttribute("FeatureNameAttributeName", node);
        }

        protected override void OnLoad(EventArgs e)
        {
            Assert.ArgumentNotNull(e, "e");
            base.OnLoad(e);
            if (Context.ClientPage.IsEvent)
            {
                return;
            }

            _linkExtendForm.LoadControls(CustomLinkAttributes,ref FeatureName);
        }

        protected override void OnOK(object sender, EventArgs args)
        {
            Assert.ArgumentNotNull(sender, "sender");
            Assert.ArgumentNotNull(args, "args");
            string path = GetPath();
            string attributeFromValue = GetLinkTargetAttributeFromValue(Target.Value, CustomTarget.Value);
            Packet packet = new Packet("link", new string[0]);
            SetAttribute(packet, "text",Text);
            SetAttribute(packet, "linktype", "external");
            SetAttribute(packet, "url", path);
            SetAttribute(packet, "anchor", string.Empty);
            SetAttribute(packet, "title", Title);
            SetAttribute(packet, "class", Class);
            SetAttribute(packet, "target", attributeFromValue);

            SetAttribute(packet, "FeatureNameAttributeName", FeatureName);
          
            SheerResponse.SetDialogValue(packet.OuterXml);
            SheerResponse.CloseWindow();
        }
        private string GetPath()
        {
            string url = this.Url.Value;
            if (url.Length > 0 && url.IndexOf("://", StringComparison.InvariantCulture) < 0 && !url.StartsWith("/", StringComparison.InvariantCulture))
            {
                url = string.Concat("http://", url);
            }

            return url;
        }
    }
}

using Sitecore;
using Sitecore.Diagnostics;
using Sitecore.Shell.Applications.ContentEditor;
using Sitecore.Text;
using Sitecore.Web.UI.Sheer;

namespace Foundation.Universal.Extensions
{
    public class ExtendLinks : Link
    {
        public override void HandleMessage(Message message)
        {
            Assert.ArgumentNotNull((object)message, nameof(message));
            base.HandleMessage(message);
            if (message["id"] != this.ID)
                return;
            string name = message.Name;

            switch (name)
            {
                case "contentlink:externallinkextend":
                    {
                        string uri = UIUtil.GetUri("control:ExternalLinkExtendForm");
                        UrlString urlString = new UrlString(uri);
                        string strUrlString = urlString.ToString();
                        this.Insert(strUrlString);
                        break;
                    }
            }
        }
    }
}

3. Register control source

Register the control with Sitecore and to display the new custom field on the external link dialog –

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <controlSources>
		<source assembly="Foundation.Universal" namespace="Foundation.Universal.Extensions" mode="on" prefix="content"/>
    </controlSources>
  </sitecore>
</configuration>

Once the text box is available, enter any value and check the raw value to see if everything works as expected