public static string RenderFile(HtmlHelper html, BootstrapFileModel model)
        {
            if (model == null || string.IsNullOrEmpty(model.htmlFieldName)) return null;

            string validationMessage = "";
            if (model.displayValidationMessage)
            {
                string validation = html.ValidationMessage(model.htmlFieldName).ToHtmlString();
                validationMessage = new BootstrapHelpText(validation, model.validationMessageStyle).ToHtmlString();
            }
            if (model.tooltipConfiguration != null) model.htmlAttributes.AddRange(model.tooltipConfiguration.ToDictionary());
            var mergedHtmlAttrs = model.htmlAttributes.FormatHtmlAttributes().AddOrReplace("type", "File");
            if (!string.IsNullOrEmpty(model.id)) mergedHtmlAttrs.AddOrReplace("id", model.id);
            return html.TextBox(model.htmlFieldName, null, mergedHtmlAttrs).ToHtmlString() + validationMessage;
        }
        public static string RenderControlGroupFile(HtmlHelper html, BootstrapFileModel inputModel, BootstrapLabelModel labelModel)
        {
            var input = Renderer.RenderFile(html, inputModel);

            string label = Renderer.RenderLabel(html, labelModel ?? new BootstrapLabelModel
            {
                htmlFieldName = inputModel.htmlFieldName,
                metadata = inputModel.metadata,
                htmlAttributes = new { @class = "control-label" }.ToDictionary()
            });

            bool fieldIsValid = true;
            if(inputModel != null) fieldIsValid = html.ViewData.ModelState.IsValidField(inputModel.htmlFieldName);
            return new BootstrapControlGroup(input, label, ControlGroupType.textboxLike, fieldIsValid).ToHtmlString();
        }