Accessing HttpContext while processing a T4 Template

Question

We have a web-application that uses T4 templates to render pages. Pages can contain simple things like text etcetera, but they can also contain custom made modules. These modules rely on the HttpContext.Current.

However, the T4 Template is processed in a thread/domain different than my webapplication. And that’s why I cannot access the HttpContext.Current in that process.

I tried to add a property for the HttpContext to the modules, which is set in the pre processing of the template. This introduces a new problem; The T4 engine requires all classes used by the page to be [Serialized]. This is no problem, except for the System.Web.HttpContext class which cannot be serialized.

System.Runtime.Serialization.SerializationException: The type System.Web.HttpContext in assembly System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a is not marked serializable.

So, in order to solve the SerializationExeption we’d add [NonSerialized] attribute to our property.

[NonSerialized]
protected HttpContext _context = null;
public HttpContext Context
{
    get
    {
        return _context;
    }
    set
    {
        _context = value;
    }
}

But by the time the template is deserialized and processed, the Context is null ofcourse, so I get a NullReferenceException in my module.

Is there a way I can access the current HttpContext in code called from the template engine?

Answer 1

I also send this question to Microsoft, and there is a very simple solution for it.

In the custom EngineHost there is a function ProvideTemplatingAppDomain. You have to make sure your Engine returns AppDomain.CurrentDomain.

In this way, the template will be compiled and ran in the same domain as your webrequest.