Checking duplicates umbracoUrlName Umbraco 7

RegisterDuplicateUrlNameDetector.cs

public class RegisterDuplicateUrlNameDetector : ApplicationEventHandler
    {
        protected override void ApplicationStarting
                      (UmbracoApplicationBase umbracoApplication,
                       ApplicationContext applicationContext)
        {
            ContentService.Publishing += ContentServicePublishing;
        }

        static void ContentServicePublishing(IPublishingStrategy sender,
                                                    PublishEventArgs<IContent> e)
{

    foreach (var content in e.PublishedEntities){
        // get content items UrlName - (more than one content item could be being published, hence the foreach)
        var contentUrlName = content.HasProperty("umbracoUrlName") &&
                             !String.IsNullOrEmpty(content.GetValue<string>("umbracoUrlName"))
            ? content.GetValue<string>("umbracoUrlName")
            : content.Name;

        //get sibling content, eg published nodes at the same level in the tree that could contain a clashing url
        if (content.Parent().Children().Any(f=>f.Id != content.Id && f.Published))
        {
            foreach (var sibling in content.Parent().Children().Where(f => f.Id != content.Id && f.Published))
            {
            // get each sibling UrlName
              var  siblingUrlName = sibling.HasProperty("umbracoUrlName") &&
                             !String.IsNullOrEmpty(sibling.GetValue<string>("umbracoUrlName"))
            ? sibling.GetValue<string>("umbracoUrlName")
            : sibling.Name;
                // check for clash
              if (siblingUrlName.ToUrlSegment() == contentUrlName.ToUrlSegment())
                {
                    // cancel publishing
                    e.Cancel = true;
                    // bubble up a message to the UI (umbraco 7.3 only)
                    e.Messages.Add(new EventMessage("Save Cancelled", "Clash of UrlNames: " + sibling.Id + "-" + sibling.Name + " and " + content.Id + "-" + content.Name, EventMessageType.Error));
                }
            }
        }
}

}
    }