How to concatenate several MvcHtmlString instances

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).

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() + string.Concat(strings.Select(s => s.ToString())));
}

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)   

And now a shameless plug for my blog: Use TagBuilder or HtmlTags to clean up your HTML

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>"

I went for this approach:

    private static MvcHtmlString Concat(params MvcHtmlString[] items)
    {
        var sb = new StringBuilder();
        foreach (var item in items.Where(i => i != null))
            sb.Append(item.ToHtmlString());
        return MvcHtmlString.Create(sb.ToString());
    }

It's just a utility method that I use inside the classes with extension methods for HtmlHelper.

I know this is super old, but yet another way (which I find to be more elegant), is to use an overload of the String method Concat, which metadata definition is

public static String Concat(params object[] args);

that basically ToStrings each one of the objects passed in and then concatenates the results and returns the concatenated string.

So the final result would be:

var result = MvcHtmlString.Create(
    string.Concat(
        label, textbox, validation
    )
);