How can I override the @Html.LabelFor template?

I have a simple field form

<div class="field fade-label">
    @Html.LabelFor(model => model.Register.UserName)
    @Html.TextBoxFor(model => model.Register.UserName)
</div>

and this results in:

<div class="field fade-label">
    <label for="Register_UserName">Username (used to identify all services, from 4 to 30 chars)</label>
    <input type="text" value="" name="Register.UserName" id="Register_UserName">
</div>

but I want that LabelFor code append a <span> inside so I can end up having:

<label for="Register_UserName">
    <span>Username (used to identify all services, from 4 to 30 chars)</span>
</label>

How can I do this?

All examples use EditorTemplates but this is a LabelFor.

You'd do this by creating your own HTML helper.

http://www.asp.net/mvc/tutorials/creating-custom-html-helpers-cs

You can view the code for LabelFor<> by downloading the source for ASP.Net MVC and modify that as a custom helper.

---

Answer added by balexandre

public static class LabelExtensions
{
    public static MvcHtmlString LabelFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, object htmlAttributes)
    {
        return LabelFor(html, expression, new RouteValueDictionary(htmlAttributes));
    }
    public static MvcHtmlString LabelFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, IDictionary<string, object> htmlAttributes)
    {
        ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, html.ViewData);
        string htmlFieldName = ExpressionHelper.GetExpressionText(expression);
        string labelText = metadata.DisplayName ?? metadata.PropertyName ?? htmlFieldName.Split('.').Last();
        if (String.IsNullOrEmpty(labelText))
        {
            return MvcHtmlString.Empty;
        }

        TagBuilder tag = new TagBuilder("label");
        tag.MergeAttributes(htmlAttributes);
        tag.Attributes.Add("for", html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldId(htmlFieldName));

        TagBuilder span = new TagBuilder("span");
        span.SetInnerText(labelText);

        // assign <span> to <label> inner html
        tag.InnerHtml = span.ToString(TagRenderMode.Normal);

        return MvcHtmlString.Create(tag.ToString(TagRenderMode.Normal));
    }
}

I expanded upon balealexandre's answer and added in the ability to specify HTML to include both before and after your label text. I added a bunch of method overloads and comments. I hope this helps folks!

Also snagged information from here: https://stackoverflow.com/questions/5706815/html-inside-label-using-html-helper

namespace System.Web.Mvc.Html
{
    public static class LabelExtensions
    {
        /// <summary>Creates a Label with custom Html before the label text.  Only starting Html is provided.</summary>
        /// <param name="startHtml">Html to preempt the label text.</param>
        /// <returns>MVC Html for the Label</returns>
        public static MvcHtmlString LabelFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, Func<object, HelperResult> startHtml)
        {
            return LabelFor(html, expression, startHtml, null, new RouteValueDictionary("new {}"));
        }

        /// <summary>Creates a Label with custom Html before the label text.  Starting Html and a single Html attribute is provided.</summary>
        /// <param name="startHtml">Html to preempt the label text.</param>
        /// <param name="htmlAttributes">A single Html attribute to include.</param>
        /// <returns>MVC Html for the Label</returns>
        public static MvcHtmlString LabelFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, Func<object, HelperResult> startHtml, object htmlAttributes)
        {
            return LabelFor(html, expression, startHtml, null, new RouteValueDictionary(htmlAttributes));
        }

        /// <summary>Creates a Label with custom Html before the label text.  Starting Html and a collection of Html attributes are provided.</summary>
        /// <param name="startHtml">Html to preempt the label text.</param>
        /// <param name="htmlAttributes">A collection of Html attributes to include.</param>
        /// <returns>MVC Html for the Label</returns>
        public static MvcHtmlString LabelFor<TModel, TProperty>(this HtmlHelper<TModel> html, Expression<Func<TModel, TProperty>> expression, Func<object, HelperResult> startHtml, IDictionary<string, object> htmlAttributes)
        {
            return LabelFor(html, expression, startHtml, null, htmlAttributes);
        }

        /// <summary>Creates a Label with custom Html before and after the label text.  Starting Html and ending Html are provided.</summary>
        /// <param name="startHtml">Html to preempt the label text.</param>
        /// <param name="endHtml">Html to follow the label text.</param>
        /// <returns>MVC Html for the Label</returns>
        public static MvcHtmlString LabelFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, Func<object, HelperResult> startHtml, Func<object, HelperResult> endHtml)
        {
            return LabelFor(html, expression, startHtml, endHtml, new RouteValueDictionary("new {}"));
        }

        /// <summary>Creates a Label with custom Html before and after the label text.  Starting Html, ending Html, and a single Html attribute are provided.</summary>
        /// <param name="startHtml">Html to preempt the label text.</param>
        /// <param name="endHtml">Html to follow the label text.</param>
        /// <param name="htmlAttributes">A single Html attribute to include.</param>
        /// <returns>MVC Html for the Label</returns>
        public static MvcHtmlString LabelFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, Func<object, HelperResult> startHtml, Func<object, HelperResult> endHtml, object htmlAttributes)
        {
            return LabelFor(html, expression, startHtml, endHtml, new RouteValueDictionary(htmlAttributes));
        }

        /// <summary>Creates a Label with custom Html before and after the label text.  Starting Html, ending Html, and a collection of Html attributes are provided.</summary>
        /// <param name="startHtml">Html to preempt the label text.</param>
        /// <param name="endHtml">Html to follow the label text.</param>
        /// <param name="htmlAttributes">A collection of Html attributes to include.</param>
        /// <returns>MVC Html for the Label</returns>
        public static MvcHtmlString LabelFor<TModel, TProperty>(this HtmlHelper<TModel> html, Expression<Func<TModel, TProperty>> expression, Func<object, HelperResult> startHtml, Func<object, HelperResult> endHtml, IDictionary<string, object> htmlAttributes)
        {
            ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, html.ViewData);
            string htmlFieldName = ExpressionHelper.GetExpressionText(expression);
        
            //Use the DisplayName or PropertyName for the metadata if available.  Otherwise default to the htmlFieldName provided by the user.
            string labelText = metadata.DisplayName ?? metadata.PropertyName ?? htmlFieldName.Split('.').Last();
            if (String.IsNullOrEmpty(labelText))
            {
                return MvcHtmlString.Empty;
            }

            //Create the new label.
            TagBuilder tag = new TagBuilder("label");

            //Add the specified Html attributes
            tag.MergeAttributes(htmlAttributes);

            //Specify what property the label is tied to.
            tag.Attributes.Add("for", html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldId(htmlFieldName));

            //Run through the various iterations of null starting or ending Html text.
            if (startHtml == null && endHtml == null) tag.InnerHtml = labelText;
            else if (startHtml != null && endHtml == null) tag.InnerHtml = string.Format("{0}{1}", startHtml(null).ToHtmlString(), labelText);
            else if (startHtml == null && endHtml != null) tag.InnerHtml = string.Format("{0}{1}", labelText, endHtml(null).ToHtmlString());
            else tag.InnerHtml = string.Format("{0}{1}{2}", startHtml(null).ToHtmlString(), labelText, endHtml(null).ToHtmlString());

            return MvcHtmlString.Create(tag.ToString());
        }
    }
}

LabelFor is an extension method (static) and therefore cannot be overridden. You'd need to create your own Html Helper Extension method to achieve what you require.