VirtualPathProvider in MVC 5

问题

I can't seem to get a custom VirtualPathProvider working in asp.net MVC 5.

The FileExists method returns true but then the GetFile method isn't called. I believe this is because IIS takes over the request and does not let .NET handle it.

I have tried setting RAMMFAR and creating a custom handler, as in this solution https://stackoverflow.com/a/12151501/801189 but still no luck. I get a error 404.

My Custom Provider:

public class DbPathProvider : VirtualPathProvider
{
    public DbPathProvider() : base()
    {

    }

    private static bool IsContentPath(string virtualPath)
    {
        var checkPath = VirtualPathUtility.ToAppRelative(virtualPath);
        return checkPath.StartsWith("~/CMS/", StringComparison.InvariantCultureIgnoreCase);
    }

    public override bool FileExists(string virtualPath)
    {
        return IsContentPath(virtualPath) || base.FileExists(virtualPath);
    }

    public override VirtualFile GetFile(string virtualPath)
    {
        return IsContentPath(virtualPath) ? new DbVirtualFile(virtualPath) : base.GetFile(virtualPath);
    }

    public override CacheDependency GetCacheDependency(string virtualPath, IEnumerable virtualPathDependencies, DateTime utcStart)
    {
        return null;

    }

    public override String GetFileHash(String virtualPath, IEnumerable virtualPathDependencies)
    {
        return Guid.NewGuid().ToString();
    }
}

My Custom Virtual File:

public class DbVirtualFile : VirtualFile
{
    public DbVirtualFile(string path): base(path)
    {

    }

    public override System.IO.Stream Open()
    {
        string testPage = "This is a test!";
        return new System.IO.MemoryStream(System.Text.ASCIIEncoding.ASCII.GetBytes(testPage));
    }
}

web.config handler I have tried to use, without success. It currently gives error 500 :

<system.webServer>
<modules runAllManagedModulesForAllRequests="true">
  <remove name="FormsAuthenticationModule" />
</modules>

<handlers>
  <add name="ApiURIs-ISAPI-Integrated-4.0"
 path="/CMS/*"
 verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS"
 type="System.Web.Handlers.TransferRequestHandler"
 preCondition="runtimeVersionv4.0" />
</handlers>

If I try to navigate to site.com/CMS/Home/Index, the FileExists method is called but strangely, the virtualPath parameter recieves only ~/CMS/Home.

Adding breakpoints, it seems that for the url site.com/CMS/Home/Index, the FileExists method keeps getting repeatedly called. This may be causing an infinite recursion, giving the internal server error.

回答1:

It was actually nothing to do with IIS, and in fact confusion on the order of events. It seems I didn't understand that a routed action method must return a view, that the VirtualPathProvider will try to resolve, rather than going to the VirtualPathProvider directly.

I create a simple controller called ContentPagesController with a single GetPage action:

public class ContentPagesController : Controller
    {
        [HttpGet]
        public ActionResult GetPage(string pageName)
        {
            return View(pageName);
        }
    }

I then set up my route to serve virtual pages:

routes.MapRoute(
 name: "ContentPageRoute",
 url: "CMS/{*pageName}",
 defaults: new { controller = "ContentPages", action = "GetPage" },
 constraints: new { controller = "ContentPages", action = "GetPage" }
);

I register my custom VirtualPathProvider before I register my routes, in globals.asax.cs.

Now suppose I have a page in my database with the relative url /CMS/Home/AboutUs. The pageName parameter will have value Home/AboutUs and the return View() call will instruct the VirtualPathProvider to look for variations of the file ~/Views/ContentPages/Home/AboutUs.cshtml.

A few of the variations it will be look for include:

~/Views/ContentPages/Home/AboutUs.aspx
~/Views/ContentPages/Home/AboutUs.ascx
~/Views/ContentPages/Home/AboutUs.vbhtml

All you now need to do is check the virtualPath that is passed to the GetFiles method, using a database lookup or similar. Here is a simple way:

private bool IsCMSPath(string virtualPath)
        {
           return virtualPath == "/Views/ContentPages/Home/AboutUs.cshtml" || 
                virtualPath == "~/Views/ContentPages/Home/AboutUs.cshtml"; 
        }

        public override bool FileExists(string virtualPath)
        {
            return IsCMSPath(virtualPath) || base.FileExists(virtualPath);
        }

        public override VirtualFile GetFile(string virtualPath)
        {
            if (IsCMSPath(virtualPath))
            {
                return new DbVirtualFile(virtualPath);
            }

            return base.GetFile(virtualPath);
        }

The custom virtual file will be made and returned to the browser in the GetFile method.

Finally, a custom view engine can be created to give different virtual view paths that are sent to VirtualPathProvider.

Hope this helps.

来源：https://stackoverflow.com/questions/24237123/virtualpathprovider-in-mvc-5