Here's a helper I wrote that adds an '*' to a label if the model property is marked as required. ModelMetaData has an IsReadonly property to might be able to leverage. You should be able to make the correct substitutions to make the changes for a textbox.
public static class LabelExtensions
{
public static MvcHtmlString LabelFor<TModel, TValue>(this HtmlHelper<TModel> html,
Expression<Func<TModel, TValue>> expression, IDictionary<String, Object> htmlAttributes,
String requiredMarker = "*")
{
return LabelHelper(html, ModelMetadata.FromLambdaExpression(expression, html.ViewData),
ExpressionHelper.GetExpressionText(expression), null, htmlAttributes, requiredMarker);
}
public static MvcHtmlString LabelFor<TModel, TValue>(this HtmlHelper<TModel> html,
Expression<Func<TModel, TValue>> expression, Object htmlAttributes, String requiredMarker)
{
return LabelFor(html, expression, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes), requiredMarker);
}
internal static MvcHtmlString LabelHelper(HtmlHelper html, ModelMetadata metadata, String htmlFieldName,
String labelText = null, IDictionary<String, Object> htmlAttributes = null, String requiredMarker = null)
{
var resolvedLabelText = labelText ??
metadata.DisplayName ?? metadata.PropertyName ?? htmlFieldName.Split('.').Last();
var tag = new TagBuilder("label");
tag.Attributes.Add("for",
TagBuilder.CreateSanitizedId(html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(htmlFieldName)));
tag.SetInnerText(resolvedLabelText);
tag.MergeAttributes(htmlAttributes, true);
if (metadata.IsRequired && !String.IsNullOrWhiteSpace(requiredMarker))
{
var requiredSpan = new TagBuilder("span") {InnerHtml = requiredMarker};
requiredSpan.AddCssClass("required");
tag.InnerHtml += requiredSpan;
}
var result = tag.ToString(TagRenderMode.Normal);
return new MvcHtmlString(result);
}
}