How to extend MVC3 Label and LabelFor HTML helpers

问题:

Html.Label and Html.LabelFor helper methods do not support the htmlAttributes parameter like most of the other helpers do. I would like to set the class however. Something like this:

Html.LabelFor(model => model.Name, new { @class = "control-label" })

Is there an easy way of extending Label/LabelFor without resorting to copying and extending the ILSpy disasm output of those methods?

回答1:

You can easily extend the label by creating your own LabelFor:

Something like this should do what you need

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

Update To use the extension method just created in your project, add this line in your Views\web.config

<pages>
  <namespaces>
    <add namespace="System.Web.Helpers" />
    <add namespace="System.Web.Mvc" />
    <add namespace="System.Web.Mvc.Ajax" />
    <add namespace="System.Web.Mvc.Html" />
    <add namespace="System.Web.Routing" />
    <add namespace="System.Web.WebPages" />
    <add namespace="MyProject.Helpers" />   <-- my extension

    ...

 </namespaces>
</pages>

回答2:

public static class LabelExtensions
{
    public static IHtmlString LabelFor<TModel, TProperty>(
        this HtmlHelper<TModel> htmlHelper,
        Expression<Func<TModel, TProperty>> expression,
        string labelText,
        object htmlAttributes
    )
    {
        var metadata = ModelMetadata.FromLambdaExpression<TModel, TProperty>(expression, htmlHelper.ViewData);
        var htmlFieldName = ExpressionHelper.GetExpressionText(expression);
        return LabelHelper(htmlHelper, metadata, htmlFieldName, labelText, htmlAttributes);
    }

    public static IHtmlString Label(this HtmlHelper htmlHelper, string expression, string labelText, object htmlAttributes)
    {
        var metadata = ModelMetadata.FromStringExpression(expression, htmlHelper.ViewData);
        return LabelHelper(htmlHelper, metadata, expression, labelText, htmlAttributes);
    }

    private static IHtmlString LabelHelper(HtmlHelper html, ModelMetadata metadata, string htmlFieldName, string labelText, object htmlAttributes)
    {
        string str = labelText ?? (metadata.DisplayName ?? (metadata.PropertyName ?? htmlFieldName.Split(new char[] { '.' }).Last<string>()));
        if (string.IsNullOrEmpty(str))
        {
            return MvcHtmlString.Empty;
        }
        TagBuilder tagBuilder = new TagBuilder("label");
        tagBuilder.Attributes.Add("for", TagBuilder.CreateSanitizedId(html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(htmlFieldName)));
        var attributes = new RouteValueDictionary(htmlAttributes);
        tagBuilder.MergeAttributes(attributes);
        tagBuilder.SetInnerText(str);
        return new HtmlString(tagBuilder.ToString(TagRenderMode.Normal));
    }
}

and then:

@Html.LabelFor(x => x.SomeProperty, null, new { @class = "foo" })

or:

@Html.Label("SomeProperty", null, new { @class = "foo" })