Question

Is there an equivalent method to MvcHtmlString in .Net 3.5 and lower? I have googled and have not found an answer. I created a helper for MVC 3/.NET 4 that uses MvcHtmlString. However it only runs on .NET 4. I want to code a version of the helper so it can run on Mvc 2/.net 3.5 so i can use the helper on another project which uses this runtime. Would i just use stringbuilder and return Stringbuilder.ToString?

Answer 1

MvcHtmlString does work on both .NET 3.5 and .NET 4 – it has a static Create() method that should be used to create a new instance.

The reason for the static factory method is so that runtime inspection can be used to determine if the environment is .NET 4 or .NET 3.5; if the environment is .NET 4, then a new type is declared at runtime that derives from MvcHtmlString and implements IHtmlString so that the new <%: %> response write with encoding syntax works.

The source code for this looks like (taken from the MVC 2 Source code)

// in .NET 4, we dynamically create a type that subclasses MvcHtmlString and implements IHtmlString
private static MvcHtmlStringCreator GetCreator()
{
    Type iHtmlStringType = typeof(HttpContext).Assembly.GetType("System.Web.IHtmlString");
    if (iHtmlStringType != null)
    {
        // first, create the dynamic type
        Type dynamicType = DynamicTypeGenerator.GenerateType("DynamicMvcHtmlString", typeof(MvcHtmlString), new Type[] { iHtmlStringType });

        // then, create the delegate to instantiate the dynamic type
        ParameterExpression valueParamExpr = Expression.Parameter(typeof(string), "value");
        NewExpression newObjExpr = Expression.New(dynamicType.GetConstructor(new Type[] { typeof(string) }), valueParamExpr);
        Expression<MvcHtmlStringCreator> lambdaExpr = Expression.Lambda<MvcHtmlStringCreator>(newObjExpr, valueParamExpr);
        return lambdaExpr.Compile();
    }
    else
    {
        // disabling 0618 allows us to call the MvcHtmlString() constructor
#pragma warning disable 0618
        return value => new MvcHtmlString(value);
#pragma warning restore 0618
    }
}