How to make if dependent HtmlHelper usage

Question

Im using asp.net mvc 2.0. I have the following HtmlHelper extension:

AdminOnly(HtmlHelper helper, IPrincipal User, string htmlToRender)
{
   //Render Html if have admin access.
}

I need to modify it to use in such a way: AdminOnly(User).TextBoxFor(x=>x.MyField) So that it could render edit field for MyField only if user has admin access.

---

For now Ive come out with the following solution:

AdminOnly(this MvcHtmlString resString, IPrincipal User)
{
   //Render Html if have admin access.
}

So in code I can write things like:

<%:Html.TextBoxFor(x=>x.MyProperty).AdminOnly(User)%>

It works but I would like to be able to add more inputs or more flexibility to add text before and after the inputs, like this:

<%:Html.PlainText("Set your age: ").TextBoxFor(x=>x.Age).AdminOnly(User)%>

or

<%: Html.AdminOnly("Set your age: ", User).AddTextBoxFor(x=>x.Age)%>

Answer 1

1) If you don't expect rendering stuff for other than current identity and you are using Thread.CurrentPrincipal I'd recommend to leave out the user parameter and using HttpContext.Current.User or Thread.CurrentPrincipal.

2) Using chained method calls would probably require quite a bit of work, instead I recommend taking advantage of lambda expressions.

Extension:

public static MvcHtmlString AdminOnly(this HtmlHelper htmlHelper, Func<MvcHtmlString> action)
{
    if (HttpContext.Current.User.IsInRole("admin"))
        return action();

    return MvcHtmlString.Empty;
}

Usage:

<%: Html.AdminOnly(() => Html.TextBoxFor(m => m.Field)) %>

edit: updated for mvc 2