How to concatenate several MvcHtmlString instances

Question

I have some doubts about how to concatenate MvcHtmlString instances because of this information found in MSDN :

MvcHtmlString Class Represents an HTML-encoded string that should not be encoded again

Do I risk that strings are HTML-encoded twice when using code like this:

var label = Html.LabelFor(model => model.Email);
var textbox = Html.TextBoxFor(model => model.Email);
var validation = Html.ValidationMessageFor(model => model.Email);

var result = MvcHtmlString.Create(
  label.ToString() + textbox.ToString() + validation.ToString());

(note: this is supposed to go into an HtmlHelper extension method to reduce code-duplication in views).

Answer 1

Your code is correct.

That snippet from MSDN means that an encoding View Engine (such as the Aspx view engine in .NET 4 when using <%: %> or the Razor view engine in MVC 3) should not re-encode the string value of the object.

So for example:

string s = "<tag>";
var hs = MvcHtmlString.Create(s);

<%: s %>  -- outputs "&lt;tag&gt;"
<%: hs %> -- outputs "<tag>"

Answer 2

Too bad C# won't let us override the + operator here! How about using an extension method instead?

public static MvcHtmlString Concat(this MvcHtmlString first, params MvcHtmlString[] strings)
{
    return MvcHtmlString.Create(first.ToString().Concat(strings.Select(s => s.ToString()).ToArray()));
}

This could probably be optimized, but you can run with it. It should be fairly trivial to prove that this doesn't double encode strings with a unit test.

Usage sample:

label.Concat(textbox, validation)   

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