How to write HtmlHelper in Fluent syntax

Question

I have a simple tag builder that looks like this:

public static MvcHtmlString Tag(this HtmlHelper helper, string tag, string content)
{
    var tagBuilder = new TagBuilder(tag){InnerHtml = content};
    return MvcHtmlString.Create(tagBuilder.ToString(TagRenderMode.NormalTag));
}

And, I can use it like this:

@Html.Tag("em", Model.Title)

which produces:

<em>The Title</em>

How can this be written to use a Fluent Syntax so it's use would look like this:

@Html.Tag("em").Content(Model.Title)

Answer 1

You have to define a builder interface and implementation. I hope my example can provide some guidance:

public static class MyHtmlExtensions
{
    public static IMyTagBuilder Tag(this HtmlHelper helper, string tag)
    {
        return new MyTagBuilder(tag);
    }
}

Then you define your builder interface and implementation:

public interface IMyTagBuilder : IHtmlString
{
    IHtmlString Content(string content);
}

public class MyTagBuilder : IMyTagBuilder
{
    private readonly TagBuilder _tagBuilder;

    public MyTagBuilder(string tag)
    {
        _tagBuilder = new TagBuilder(tag);
    }

    public IHtmlString Content(string content)
    {
        _tagBuilder.InnerHtml = content;
        return this;
    }

    public string ToHtmlString()
    {
        return _tagBuilder.ToString(TagRenderMode.NormalTag);
    }
}

Since IMyTagBuilder implements IHtmlString, it can be used either with or without calling .Content() afterwards.

A great trick to use when implementing fluent interfaces it to use a IFluentInterface to hide object members (ToString, Equals, GetHashCode and GetType) from IntelliSense, it removes some noise.

EDIT: A great resource for building fluent APIs is Daniel Cazzulino's screencast from building Funq here