Register Custom ASP.NET MVC Routes in Sitecore

Sitecore allows custom ASP.NET MVC routes to be used on a Sitecore site.

However, improper adding of such routes may lead to different problems with using Sitecore Client, such as broken dialogues, non-functioning buttons, etc.

For example, this may be the result of defining custom routes in the Global.asax file, causing conflicts with a number of default routes defined by Sitecore and used for Sitecore Client functionality.

You can also find more information about ASP.NET Routing in the following article:
https://msdn.microsoft.com/en-us/library/cc668201.aspx

Follow the steps below to define custom ASP.NET MVC routes in a way that does not conflict with the default Sitecore routes.

Create a custom processor for the initialize pipeline and define a custom route in the Process method similar to the following:

public class RegisterCustomRoute

{

  public virtual void Process(PipelineArgs args)

  {

    RouteTable.Routes.MapRoute("CustomRoute", "some/route/{controller}/{action}/{id}");

  }

}

Add this processor to the initialize pipeline right before the Sitecore InitializeRoutes processor. You can do this with the help of the configuration patch file in the following way:

<?xml version="1.0" encoding="utf-8"?>

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">

     <sitecore>

          <pipelines>

               <initialize>

                    <processor type="MyNamespace.RegisterCustomRoute, MyAssembly" patch:before="processor[@type='Sitecore.Mvc.Pipelines.Loader.InitializeRoutes, Sitecore.Mvc']" />

               </initialize>

          </pipelines>

     </sitecore>

</configuration>

Important: ensure your custom configuration patch file is applied as the last patch to Sitecore configuration.
You can do this by placing the patch file into a subfolder of the /App_Config/Include directory. The name of the subfolder must be the last one alphabetically related to other subfolders (such as Z_CustomConfigs).