TagBuilder.MergeAttributes does not work

I am creating my own helper in MVC. But the custom attributes are not added in the HTML:

Helper

public static MvcHtmlString MenuItem(this HtmlHelper helper, string linkText, string actionName, string controllerName, object htmlAttributes)
{
    var currentControllerName = (string)helper.ViewContext.RouteData.Values["controller"];
    var currentActionName = (string)helper.ViewContext.RouteData.Values["action"];

    var builder = new TagBuilder("li");

    if (currentControllerName.Equals(controllerName, StringComparison.CurrentCultureIgnoreCase)
        && currentActionName.Equals(actionName, StringComparison.CurrentCultureIgnoreCase))
        builder.AddCssClass("selected");

    if (htmlAttributes != null)
    {
        var attributes = new RouteValueDictionary(htmlAttributes);
        builder.MergeAttributes(attributes, false); //DONT WORK!!!
    }

    builder.InnerHtml = helpe开发者_StackOverflowr.ActionLink(linkText, actionName, controllerName).ToHtmlString();
    return MvcHtmlString.Create(builder.ToString(TagRenderMode.Normal));
}

CSHTML

@Html.MenuItem("nossa igreja2", "Index", "Home", new { @class = "gradient-top" })

Final result (HTML)

<li class="selected"><a href="/">nossa igreja2</a></li>

Note that it did not add the class gradient-top that I mentioned in the helper call.

When calling MergeAttributes with replaceExisting set to false, it just adds the attributes that do not currently exist in the the attributes dictionary. It does not merge/concat the values of individual attributes.

I believe moving your call to

builder.AddCssClass("selected");

after

builder.MergeAttributes(attributes, false);

will fix your problem.

I wrote this extension method that does what I thought MergeAttributes was supposed to do (but upon checking the source code it just skips existing attributes):

public static class TagBuilderExtensions
{
    public static void TrueMergeAttributes(this TagBuilder tagBuilder, IDictionary<string, object> attributes)
    {
        foreach (var attribute in attributes)
        {
            string currentValue;
            string newValue = attribute.Value.ToString();

            if (tagBuilder.Attributes.TryGetValue(attribute.Key, out currentValue))
            {
                newValue = currentValue + " " + newValue;
            }

            tagBuilder.Attributes[attribute.Key] = newValue;
        }
    }
}