Razor view engine is hard to customize

[talmroth]

In MVC5 we created a custom view engine that had some customizations to allow for custom view location formats. In MVC we were able to change the strings for the patterns but still had to do additional work to to process them. In MVC6 everything looks to be private/readonly and we cannot do the same customization.

here is our MVC5 implementation:

using System.Web.Mvc;

namespace CustomViewEngine
{
    //THIS VIEW ENGINE DOES NOT HANDLE AREAS.
    internal sealed class CustomLookupViewEngine : RazorViewEngine
    {
        public CustomLookupViewEngine()
        {
            ViewLocationFormats = new[]
            {
                "~/Views/%1/{1}/{0}.cshtml",
                "~/Views/%1/Shared/{0}.cshtml",
                "~/Views/Default/{1}/{0}.cshtml",
                "~/Views/Default/Shared/{0}.cshtml",
            };

            MasterLocationFormats = new[]
            {
                "~/Views/%1/{1}/{0}.cshtml",
                "~/Views/%1/Shared/{0}.cshtml",
                "~/Views/Default/{1}/{0}.cshtml",
                "~/Views/Default/Shared/{0}.cshtml",
            };

            PartialViewLocationFormats = new[]
            {
                "~/Views/%1/{1}/{0}.cshtml",
                "~/Views/%1/Shared/{0}.cshtml",
                "~/Views/Default/{1}/{0}.cshtml",
                "~/Views/Default/Shared/{0}.cshtml",
            };
        }

        protected override IView CreatePartialView(ControllerContext controllerContext, string partialPath)
        {
            var siteCode = GeValue(controllerContext, "siteCode");
            return base.CreatePartialView(controllerContext, partialPath.Replace("%1", siteCode));
        }


        protected override IView CreateView(ControllerContext controllerContext, string viewPath, string masterPath)
        {
            var siteCode = GeValue(controllerContext, "siteCode");
            return base.CreateView(controllerContext, viewPath.Replace("%1", siteCode), masterPath.Replace("%1", siteCode));
        }


        protected override bool FileExists(ControllerContext controllerContext, string virtualPath)
        {
            var siteCode = GeValue(controllerContext, "siteCode");
            return base.FileExists(controllerContext, virtualPath.Replace("%1", siteCode));
        }

        private static string GeValue(ControllerContext controllerContext, string key)
        {
            var result = ValueProviderFactories.Factories.GetValueProvider(controllerContext).GetValue(key);
            return result == null ? null : result.AttemptedValue;
        }
    }

}

[ghstahl]

duplicate of #817

[yishaigalatzer]

This looks like a dup, but it highlights more issues with the design, where here the user wants more token replacements.

We will consider a single fix for both issues.

[pranavkm]

The changes made as part of ViewLocationExpanders largely covers the scenarios that you're trying to get to. ViewLocationFormats and AreaViewLocationFormats have also been made virtual in case you want to use the traditional route of subtyping the view engine although we recommend using expanders instead.

#1212 is meant for tracking some additional enhancement to the changes in #1039.