在MVC中清除视图引擎会破坏站点地图的面包屑样式

Question

In a MVC 5 web application that i am developing, for performance sake i am clearing the view engines and adding only the RazorViewEngine in Global.asax.cs using ViewEngines.Engines.Clear(); and it breaks the styles in the mvc sitemap breadcrumbs

Before

After

My sitemap partial view (SiteMapPathHelperModel.cshtml) looks like

@model MvcSiteMapProvider.Web.Html.Models.SiteMapPathHelperModel
@using System.Web.Mvc.Html
@using System.Linq
@using MvcSiteMapProvider.Web.Html.Models
<ol class="breadcrumb">
    @foreach (var node in Model)
    {
        if (node == Model.Last())
        {
            <li class="active">
                <strong>@Html.DisplayFor(m => node)</strong>
            </li>
        }
        else
        {
            <li>
                @if (node.Title == "Home")
                {
                    <a href="/"><i class="fa fa-lg fa-home"></i></a>

                }
                else
                {
                    @Html.DisplayFor(m => node)
                }
            </li>
        }
    }
</ol>

Somehow it appears to be falling back to another implementation than the partials under views > shared > display templates

What could be the cause?

Edit

I've missed some vital info here, another dev has done this at the bottom of the Application_Start()

ViewEngines.Engines.Add(new RazorViewEngine
{
     PartialViewLocationFormats = new string[]
     {
           "~/Areas/Shared/{0}.cshtml",
     }
});

Answer 1

I'm not seeing an issue with the information you provided, but my guess is that you are not clearing and setting the view engines inside of the Application_Start method.

public class MvcApplication : System.Web.HttpApplication
{
    protected void Application_Start()
    {
        ViewEngines.Engines.Clear();
        ViewEngines.Engines.Add(new RazorViewEngine());

        AreaRegistration.RegisterAllAreas();
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);
        BundleConfig.RegisterBundles(BundleTable.Bundles);
    }
}

Note that the internal MvcSiteMapProvider engine is for backup when there are no views in your /Views/Shared/DisplayTemplates/ folder. It will serve the default template from within the DLL in this case, which is what appears to be happening here.

That could happen if your Razor view engine is registered after the internal view engine. So, if you don't have this code in Application_Start (as you should), then you could try to insert the Razor view engine to ensure it is placed before the MvcSiteMapProvider fallback engine.

ViewEngines.Engines.Clear();
ViewEngines.Engines.Insert(0, new RazorViewEngine());

Or as already mentioned, just remove the web page view engine in a single action.

ViewEngines.Engines.RemoveAt(0);

The internal view engine is registered the first time a MvcSiteMapProvider HTML helper is called. So if you are calling the add method after that point, you are adding the Razor view engine after the internal MvcSiteMapProvider view engine.

Answer 2

When the MvcSiteMapProvider is loaded, it uses its own ViewEngine. I suspect you are removing it.

Try adding a new MvcSiteMapProvider.Web.Mvc.MvcSiteMapProviderViewEngine() object to the list of ViewEngines.

Answer 3

Thanks NightOwl and Rowan

The solution was to add "~/Views/Shared/{0}.cshtml" as an item in PartialViewLocationFormats

  ViewEngines.Engines.Add(new RazorViewEngine
            {
                PartialViewLocationFormats = new string[]
                {
                    "~/Areas/Shared/{0}.cshtml",
                    "~/Views/{1}/{0}.cshtml"
                    "~/Views/Shared/{0}.cshtml",
                }
            });