.Net MVC TextBoxFor 扩展 placeholder 与 class 属性

namespace System.Web.Mvc
{
    public static class HtmlHelperExtensions
    {
        public static MvcHtmlString BsTextBoxFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, string placeholder,string @class)
        {
            TagBuilder tagBuilder = new TagBuilder("input");
            ModelMetadata metadata = ModelMetadata.FromLambdaExpression<TModel, TProperty>(expression, htmlHelper.ViewData);
            string name = ExpressionHelper.GetExpressionText(expression);
            tagBuilder.GenerateId(name);
            tagBuilder.MergeAttribute("name", name, true);
            tagBuilder.MergeAttribute("type", "text");
            tagBuilder.MergeAttribute("placeholder", placeholder); 
            tagBuilder.MergeAttributes<string, object>(htmlHelper.GetUnobtrusiveValidationAttributes(name, metadata)); 
            tagBuilder.AddCssClass(@class);
            return new MvcHtmlString(tagBuilder.ToString());
        }
    }
}