Question

I have currently created an extension method

using System.Web;
 using System.Web.Mvc;

  namespace Mobi.QualityControl.Site.Infrastructure
{
public static class HtmlHelpers
{
    public static HtmlString ActionImage(this HtmlHelper htmlHelper, string action, object routeValues, string imagePath, string alt)
    {
        var url = new UrlHelper(htmlHelper.ViewContext.RequestContext);

        // build the <img> tag
        var imgBuilder = new TagBuilder("img");
        imgBuilder.MergeAttribute("src", url.Content(imagePath));
        imgBuilder.MergeAttribute("alt", alt);
        string imgHtml = imgBuilder.ToString(TagRenderMode.SelfClosing);

        // build the <a> tag
        var anchorBuilder = new TagBuilder("a");
        anchorBuilder.MergeAttribute("href", url.Action(action, routeValues));
        anchorBuilder.InnerHtml = imgHtml; // include the <img> tag inside
        string anchorHtml = anchorBuilder.ToString(TagRenderMode.Normal);
        return new HtmlString(anchorHtml);
    }
}

}

I am then trying to use it in my page with the using statement in my web.config and it is picking the method up but it

@HtmlHelpers.ActionImage(“Account/Register”, “/images/home/gettingstarted.png”, “Edit”, “GettingStarted”)

It says it still requires 5 parameters not 4.

It is probably something very simple. Any help would be appreciated.

Answer 1

No, you are not calling your helper correctly. It should be like this:

@Html.ActionImage("Account/Register", "/images/home/gettingstarted.png", "Edit", "GettingStarted")

Html helpers in ASP.NET MVC are nothing more than extension methods in C# which I invite you to familiarize yourself with before getting into ASP.NET MVC.

Basically in C#, extension methods are invoked on an instance of the class they are extending. In your case that’s the HtmlHelper class. A Razor view has a property called Html which is of type HtmlHelper. So you invoke the extension method on it:

@Html.SOME_EXTENSION_METHOD_THAT_IS_BROUGHT_INTO_SCOPE_BY_A_USING_DIRECTIVE(...)

Of course extension methods are nothing more than static methods that you could also invoke like this (it is wrong, please never invoke an extension method like that – it’s not what and how extension methods were designed for):

@HtmlHelpers.ActionImage(Html, "Account/Register", "/images/home/gettingstarted.png", "Edit", "GettingStarted")

Notice how I am passing Html as first argument of the static method. But never use that.