如何从Razor视图中调用带有可选参数的辅助方法？

Question

I've created a new html helper method for creating image tags within the razor view engine:

    public static MvcHtmlString Image(this HtmlHelper helper, string fileName, string altText, 
        string cssClass = null, string id = null, string style = null)
    {
        var server = HttpContext.Current.Server;
        string location = server.MapPath("~/Content/Images/" + fileName);
        var builder = new TagBuilder("img");
        builder.Attributes["src"] = location;
        builder.Attributes["alt"] = altText;

        if (!string.IsNullOrEmpty(cssClass))    builder.Attributes["class"] = cssClass;
        if (!string.IsNullOrEmpty(id))          builder.Attributes["id"] = id;
        if (!string.IsNullOrEmpty(style))       builder.Attributes["style"] = style;

        string tag = builder.ToString(TagRenderMode.SelfClosing);
        return new MvcHtmlString(tag);
    }

I think that the method is probably working, but I'm having problems calling it. From within my view, I have:

@Html.Image("getstarted-promo.jpg", "Get Started", style = "width: 445; height: 257;")

When the view loads, I get this compiler error:

CS0103: The name 'style' does not exist in the current context

What is the correct syntax for using optional parameters within a razor view?

Answer 1

You are not using a valid C# syntax. Use : instead of = to specify the value of an optional argument:

@Html.Image("getstarted-promo.jpg", "Get Started", style: "width: 445; height: 257;")

Further reading: Named and Optional Arguments (C# Programming Guide)