Resolving Conflicts between Local Assemblies and the GAC in ASP.NET MVC
When upgrading from ASP.NET MVC 3 to ASP.NET MVC 4, developers may encounter an error that prevents the application from running smoothly. This error occurs due to a conflict between the local assemblies and the Global Assembly Cache (GAC). In this article, we will delve into the root cause of this issue and provide a step-by-step guide on how to resolve it.
The Error Message
The error message typically appears as follows:
[A] System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to [B] System.Web.WebPages.Razor.Configuration.HostSection.
Type A originates from 'System.Web.WebPages.Razor, Version = 1.0.0.0, Culture = neutral, PublicKeyToken = 31bf3856ad364e35' in the context 'Default' at location 'C:\WINDOWS\Microsoft.NET\assembly\GAC_MSIL\System.Web.WebPages.Razor\v4.0_1.0.0.0__31bf3856ad364e35\System.Web.WebPages.Razor.dll'.
Type B originates from 'C:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\root\7c2060f6\6145b34e\assembly\dl3\9036b7c7\fc8023c0_73fecb01\System.Web.WebPages.Razor.DLL'.
The Root Cause
The root cause of this issue lies in the conflict between the local assemblies and the GAC. When the application is upgraded from ASP.NET MVC 3 to ASP.NET MVC 4, the local assemblies and the GAC may contain different versions of the same assembly. This conflict can lead to the error message mentioned above.
Resolving the Conflict
To resolve this conflict, we need to modify the web.config file to point to the correct version of the assembly. We can do this by adding a configuration node in the web.config file located in the Views folder.
Modifying the Web.config File
The modified web.config file should look like this:
<?xml version="1.0"?>
<configuration>
<configSections>
<sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
<section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
<section name="pages" type="System.Web.WebPages.Razor.Configuration.RazorPagesSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
</sectionGroup>
</configSections>
<system.web.webPages.razor>
<host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=4.0.0.0, 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.Optimization" />
<add namespace="System.Web.Routing" />
</namespaces>
</pages>
</system.web.webPages.razor>
<appSettings>
<add key="webpages:Enabled" value="false" />
</appSettings>
<system.web>
<httpHandlers>
<add path="*" verb="*" type="System.Web.HttpNotFoundHandler" />
</httpHandlers>
<pages validateRequest="false" pageParserFilterType="System.Web.Mvc.ViewTypeParserFilter, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" pageBaseType="System.Web.Mvc.ViewPage, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" userControlBaseType="System.Web.Mvc.ViewUserControl, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
<controls>
<add assembly="System.Web.Mvc, Version=4.0.0.0, 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>
Modifying the Web.config File in the Views Folder
The modified web.config file in the Views folder should look like this:
<?xml version="1.0"?>
<configuration>
<configSections>
<sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
<section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
<section name="pages" type="System.Web.WebPages.Razor.Configuration.RazorPagesSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
</sectionGroup>
</configSections>
<system.web.webPages.razor>
<host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=4.0.0.0, 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.Optimization" />
<add namespace="System.Web.Routing" />
</namespaces>
</pages>
</system.web.webPages.razor>
<system.web>
<compilation debug="true" targetFramework="4.0">
<assemblies>
<add assembly="System.Web.Abstractions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Web.Helpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Web.WebPages, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
</assemblies>
</compilation>
<authentication mode="Forms" />
<pages>
<namespaces>
<add namespace="System.Web.Helpers" />
<add namespace="System.Web.Mvc" />
<add namespace="System.Web.Mvc.Ajax" />
<add namespace="System.Web.Mvc.Html" />
<add namespace="System.Web.Routing" />
<add namespace="System.Web.WebPages" />
</namespaces>
</pages>
</system.web>
</configuration>
Conclusion
In conclusion, the conflict between the local assemblies and the GAC in ASP.NET MVC can be resolved by modifying the web.config file to point to the correct version of the assembly. By following the steps outlined in this article, developers can resolve this issue and ensure that their application runs smoothly.