How to validate custom ASP.NET MVC helper

Question

I need to get working validation of the custom ASP.NET MVC helper.

Helper

public static class AutocompleteHelper
{
    public static MvcHtmlString AutocompleteFor<TModel, TValue>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression, string actionUrl)
    {
        return CreateAutocomplete(helper, expression, actionUrl, null, null);
    }
    public static MvcHtmlString AutocompleteFor<TModel, TValue>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression, string actionUrl, bool? isRequired, string placeholder)
    {

        return CreateAutocomplete(helper, expression, actionUrl, placeholder, isRequired);
    }

    private static MvcHtmlString CreateAutocomplete<TModel, TValue>(HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression, string actionUrl, string placeholder, bool? isRequired)
    {
        var attributes = new Dictionary<string, object>
                             {
                                 { "data-autocomplete", true },
                                 { "data-action", actionUrl }
                             };

        if (!string.IsNullOrWhiteSpace(placeholder))
        {
            attributes.Add("placeholder", placeholder);
        }

        if (isRequired.HasValue && isRequired.Value)
        {
            attributes.Add("required", "required");
        }

        attributes.Add("class", "form-control formControlAutocomplete");


        attributes.Add("maxlength", "45");


        Func<TModel, TValue> method = expression.Compile();
        var value = method((TModel)helper.ViewData.Model);
        var baseProperty = ((MemberExpression)expression.Body).Member.Name;
        var hidden = helper.Hidden(baseProperty, value);

        attributes.Add("data-value-name", baseProperty);

        var automcompleteName = baseProperty + "_autocomplete";
        var textBox = helper.TextBox(automcompleteName, null, string.Empty, attributes);

        var builder = new StringBuilder();
        builder.AppendLine(hidden.ToHtmlString());
        builder.AppendLine(textBox.ToHtmlString());

        return new MvcHtmlString(builder.ToString());
    }
}

HTML

@Html.AutocompleteFor(x => x.ProductUID, Url.Action("AutocompleteProducts", "Requisition"), true, "Start typing Product name...")
@Html.ValidationMessageFor(x => x.ProductUID)

I seems like validating but no message appears.

Any clue?

Answer 1

The name of your text field is ProductUID_autocomplete but your ValidationMessageFor which is supposed to display the error message is bound to ProductUID.

So make sure that you are binding your error message to the same property:

@Html.ValidationMessage("ProductUID_autocomplete")

It appears that whatever custom logic you might have to validate this field is injecting the error under the ProductUID_autocomplete key in the ModelState.

This being said, why not just invoke the ValidationMessage helper inside your custom helper? This way you will have less things to type in your view and the logic with those names being suffixed with _autocomplete will stay inside the helper only.