ASP.NET MVC razor: conditional attribute in HTML

MVC has conditional attributes built in...

<div @{if (myClass != null) { <text>class="@myClass"</text> } }>Content</div>
<div class="@myClass">Content</div>

If @myClass is null, it just won't use the attribute at all...

I know that may not quite solve your current issue, but it is noteworthy!

http://weblogs.asp.net/jgalloway/archive/2012/02/16/asp-net-4-beta-released.aspx

I use a small helper method that will conditionally add an attribute if the value is non-empty, and, if defined, when a Boolean function expression evaluates to true:

public static MvcHtmlString Attr(this HtmlHelper helper, string name, string value, Func<bool> condition = null)
{
    if (string.IsNullOrEmpty(name) || string.IsNullOrEmpty(value))
    {
        return MvcHtmlString.Empty;
    }

    var render = condition != null ? condition() : true;

    return render ? 
        new MvcHtmlString(string.Format("{0}=\"{1}\"", name, HttpUtility.HtmlAttributeEncode(value))) : 
        MvcHtmlString.Empty;
}

Once defined, I can use this method in my Razor views:

<li @(Html.Attr("class", "new", () => example.isNew))>
...
</li>

The above code will render <li class="new">...</li> if example.isNew == true, if not will omit the entire class attribute.

<li class="@(ViewBag.pagename == "Business details" ? "active" : null)">  

You should replace the inline style="..." with a separate classname and use the same syntax there.

However, it would be cleaner to make a separate HTML helper extension method that takes a page and action name and generates the HTML generically.