MVC5 HTMLHelper extension does not return expected content

Question

I'm looking to augment the "Html.TextBoxFor" extension to meet some specific client needs.

As a sanity check, I started simple, and just created a Test extension method which would simply delegate to the existing functionality:

public static class HtmlExtensions
{
    public static MvcHtmlString Test<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
    {
        return htmlHelper.TextBoxFor(expression);
    }
}

Everything seemed to work until I tried this against a model marked up with annotations, ie:

public class TestRoot
{
    [Display(Name = "Max Length 10")]
    [Required]
    [StringLength(10)]
    public string MaxLength10 { get; set; }
}

When I call the built-in TextBoxFor function, I get all expected mark-up, ie:

@Html.TextBoxFor(e=> e.MaxLength10)

<input data-val="true" data-val-length="The field Max Length 10 must be a string with a maximum length of 10." data-val-length-max="10" data-val-required="The Max Length 10 field is required." id="MaxLength10" name="MaxLength10" type="text" value="">

When I called my extension, I expected the same content, but instead I get this:

@Html.Test(e=>e.MaxLength10)

<input id="MaxLength10" name="MaxLength10" type="text" value="">

What happened to all the nice data annotation tags?

Answer 1

I have a similar extension method that creates a watermark textbox that works correctly. Give it a shot to see if it fixes your issue. Also take a look at the ModelMetadata instance to see if it is getting created correctly.

public static MvcHtmlString WatermarkTextBoxFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, object htmlAttributes = null)
{
    ModelMetadata metadata = ModelMetadata.FromLambdaExpression<TModel, TProperty>(expression, htmlHelper.ViewData);
    string watermark = !String.IsNullOrEmpty(metadata.Watermark) ? metadata.Watermark : metadata.DisplayName;
    var attributes = htmlHelper.MergeAttributes(htmlAttributes, new { placeholder = watermark });

    return htmlHelper.TextBoxFor<TModel, TProperty>(expression, attributes);
}