Question

i have wrote a extension method for customize my validation messages, like this:

 namespace Helpers
{
public static class HtmlHelpers
{
    public static MvcHtmlString ValidationMessageFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
    {
        var sb = new StringBuilder();

        string modelName = ExpressionHelper.GetExpressionText(expression);
        ModelState state = htmlHelper.ViewData.ModelState[modelName];
        if (state != null)
            if ((state.Errors != null) && (state.Errors.Count > 0))
            {
                sb.Append("<div class='error-left'></div>");
                sb.Append("<div class='error-inner'>");
                sb.Append(htmlHelper.ValidationMessageFor(expression).ToString());
                sb.Append("</div>");
            }

        return MvcHtmlString.Create(sb.ToString());
    }
}
}

So in my view, i put

@using HtmlHelpers

and also

@Html.ValidationMessageFor(model => model.Name)

But i’m getting this exception:

The call is ambiguous between the following methods or properties: 'ContinentalWeb.Helpers.HtmlHelpers.ValidationMessageFor<ContinentalWeb.Models.Maker,string>(System.Web.Mvc.HtmlHelper<Type>, System.Linq.Expressions.Expression<System.Func<Type,string>>)' and 'System.Web.Mvc.Html.ValidationExtensions.ValidationMessageFor<Type,string>(System.Web.Mvc.HtmlHelper<Type>, System.Linq.Expressions.Expression<System.Func<Type,string>>)'

I’m new in MVC… any help?

Thank you!

Answer 1

Your extension method has the same name and signature as the default one. This is not possible because you cannot have the 2 at the same time in scope. You will have to give a different name to your method or change the number and/or type of arguments to avoid the conflict.

For example:

public static MvcHtmlString CustomValidationMessageFor<TModel, TProperty>(
    this HtmlHelper<TModel> htmlHelper, 
    Expression<Func<TModel, TProperty>> expression
)
{
    ...
}

and then use it like this:

@Html.CustomValidationMessageFor(model => model.Name)