MEF and Razor Views inside Class Library

Question

I have a composite ASP .NET MVC 3 Razor application using MEF. Everything goes fine if I am to deploy plugins as DLL files and views (CSHTML) under the regular Views folder from the application. But this is not very clean and it won't be a real plugin if I don't place views as embedded resources within the DLL files (along with both controllers and models).

I've followed many articles (most of them are outdated). In fact there is one quite good one here on Stack Overflow: Controllers and Views inside a Class Library

I've also checked docs for VirtualPathProvider and I've been able to build a custom one that finds the file within the assembly and loads it perfectly (or at least gets the stream to it). For this I've followed the VirtualPathProvider documentation on MSDN.

There is also an implementation for VirtualFile but not yet for VirtualDirectory.

Here is the problem. I'm working with Razor views. I do know that they need config specs from the web.config file for Razor to build them. But if I embed them within the DLL this config is simply lost.

I wonder if that's why I keep getting the error:

The view at '~/Plugins/CRM.Web.Views.CRM.Index.cshtml' must derive from WebViewPage, or WebViewPage.

Maybe I just need to add some code to make it work? Any ideas?

Answer 1

My preferred way to embed Razor Views in a Class Library is to copy them into the MVC website's Views/Areas folders with a post build event. Custom view locations can be specified if you override the ViewEngine or VirtualPathProvider.

The tricky part for me was getting intellisense to work in these View Class libraries. First, you must add a Web.Config to your View assembly. Note that you don't have to actually include it in your assembly. It only has to be in the assembly root directory (or views folder). Here is an example. Regard the important Assemblies/Compilation section.

<?xml version="1.0"?>
<configuration>
  <configSections>
    <sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
      <section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
      <section name="pages" type="System.Web.WebPages.Razor.Configuration.RazorPagesSection, System.Web.WebPages.Razor, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
    </sectionGroup>
  </configSections>

  <system.web.webPages.razor>
    <host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
    <pages pageBaseType="System.Web.Mvc.WebViewPage">
      <namespaces>
        <add namespace="System.Web.Mvc" />
        <add namespace="System.Web.Mvc.Ajax" />
        <add namespace="System.Web.Mvc.Html" />
        <add namespace="System.Web.Routing" />
      </namespaces>
    </pages>
  </system.web.webPages.razor>

  <appSettings>
    <add key="webpages:Enabled" value="false" />
  </appSettings>

  <system.web>
    <compilation targetFramework="4.0">
      <assemblies>
        <add assembly="System.Web.Abstractions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
        <add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
        <add assembly="System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
        <add assembly="System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
        <add assembly="System.Web.WebPages, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
      </assemblies>
    </compilation>

    <httpHandlers>
      <add path="*" verb="*" type="System.Web.HttpNotFoundHandler"/>
    </httpHandlers>

    <!--
        Enabling request validation in view pages would cause validation to occur
        after the input has already been processed by the controller. By default
        MVC performs request validation before a controller processes the input.
        To change this behavior apply the ValidateInputAttribute to a
        controller or action.
    -->
    <pages
        validateRequest="false"
        pageParserFilterType="System.Web.Mvc.ViewTypeParserFilter, System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"
        pageBaseType="System.Web.Mvc.ViewPage, System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"
        userControlBaseType="System.Web.Mvc.ViewUserControl, System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
      <controls>
        <add assembly="System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" namespace="System.Web.Mvc" tagPrefix="mvc" />
      </controls>
    </pages>
  </system.web>
  <system.webServer>
    <validation validateIntegratedModeConfiguration="false" />
    <handlers>
      <remove name="BlockViewHandler"/>
      <add name="BlockViewHandler" path="*" verb="*" preCondition="integratedMode" type="System.Web.HttpNotFoundHandler" />
    </handlers>
  </system.webServer>
</configuration>

Next, you need to modify your class library's vbproj file so that all OutputPath elements point to 'bin\' instead of 'Debug\bin\' or 'Release\bin\'. This is the main difference I found between class libraries and ASP.Net web project types that can cause intellisense bugs.

If you still recieve your must inherits error, consider using @Inherits System.Web.Mvc.WebViewPage in your views. If you are not copying your views into your website project, you may be loading them from Embedded Resources using a custom ViewEngine / VirtualPathProvider. If that is the case, you definately need the Inherits so Razor knows what your view base class is unfortunately.

Good luck.