Html Helper Extensions not being found

Question

I'm using the release version of ASP.net MVC and I seem to be getting this error a lot

'System.Web.Mvc.HtmlHelper' does not contain a definition for 'RenderPartial' and no extension method 'RenderPartial' accepting a first argument of type 'System.Web.Mvc.HtmlHelper' could be found (are you missing a using directive or an assembly reference?)

which is very odd since I can browse to System.Web.Mvc.HtmlHelper and all the extension methods are there. Even stranger is that I can compile and all the errors go away, however as soon as I start editing again they show back up. I am including

<%@ Import Namespace="System.Web.Mvc" %>
<%@ Import Namespace="System.Web.Mvc.Html" %>

in my site.master file which I found suggested somewhere but that doesn't seem to help. Any ideas? The intelisense isn't finding the extension methods either.

Answer 1

Do you use

<% Html.RenderPartial("~/Views/Project/Projects.ascx", ViewData); %>

or

<%=Html.RenderPartial("~/Views/Project/Projects.ascx", ViewData); %>

?

it's supposed to be the first one, without "=". I'm not sure if that will solve it but I remember they changed something that way.

Answer 2

First, check if you are using RenderPartial method right:

<% Html.RenderPartial(...); %>

Second, check your web.config contains:

<system.web>
    <compilation>
        <assemblies>
            <add assembly="System.Web.Mvc, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
        </assemblies>
    </compilation>
    <pages>
        <namespaces>
            <add namespace="System.Web.Mvc.Html" />
        </namespaces>
    </pages>
</system.web>

Answer 3

Are you able to get to the other Html helpers? (you already answered that)

When you look at the project references, are there any errors?
What version of the Mvc release are you running against?

Answer 4

Also see: http://stackoverflow.com/questions/1780097/system-web-mvc-htmlhelper-does-not-contain-a-definition-for-renderpartial-a

You may think this is dumb, but I just had the same problem. I had a working MVC app, running 1.0.0.0 and all of a sudden it stopped working giving me the same RenderPartial isn't in the definition. Well it turns out that while I was going crazy cleaning up my web.config, I removed this section. When I re-added it, everything worked again. I'm sure this has something to do with how the class extensions load during runtime.

Anyway, re-adding this to my web.config worked on my machine. ;)

<system.codedom>
    <compilers>
        <compiler language="c#;cs;csharp" extension=".cs" warningLevel="4"
                     type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
            <providerOption name="CompilerVersion" value="v3.5"/>
            <providerOption name="WarnAsError" value="false"/>
        </compiler>

        <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" warningLevel="4"
                     type="Microsoft.VisualBasic.VBCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
            <providerOption name="CompilerVersion" value="v3.5"/>
            <providerOption name="OptionInfer" value="true"/>
            <providerOption name="WarnAsError" value="false"/>
        </compiler>
    </compilers>
</system.codedom>