Question

Is there any possible way to extend the basic html helpers (TextBoxFor, TextAreaFor, etc) using extension methods on their output, instead of just re-writing the entire methods completely? For instance, adding in …

@Html.TextBoxFor( model => model.Name ).Identity("idName")

I know I can achieve this using the following, already..

@Html.TextBoxFor( model => model.Name, new { @id = "idName" })

But that gets clunky and frustrating to manage when you have to start adding a lot of properties. Is there any way to add extensions to these inherently without just passing in htmlAttributes for every little detail?

Answer 1

As @AaronShockley says, because TextBoxFor() returns an MvcHtmlString, your only option for developing a ‘fluid API’ style of amending the output would be to operate on the MvcHtmlStrings returned by the helper methods. A slightly different way of doing this which I think approaches what you’re after would be to use a ‘property builder’ object, like this:

public class MvcInputBuilder
{
    public int Id { get; set; }

    public string Class { get; set; }
}

…and to set up extension methods like this:

public static MvcHtmlString TextBoxFor<TModel, TProp>(
    this HtmlHelper<TModel> htmlHelper,
    Expression<Func<TModel, TProp>> expression,
    params Action<MvcInputBuilder>[] propertySetters)
{
    MvcInputBuilder builder = new MvcInputBuilder();

    foreach (var propertySetter in propertySetters)
    {
        propertySetter.Invoke(builder);
    }

    var properties = new RouteValueDictionary(builder)
        .Select(kvp => kvp)
        .Where(kvp => kvp.Value != null)
        .ToDictionary(kvp => kvp.Key, kvp => kvp.Value);

    return htmlHelper.TextBoxFor(expression, properties);
}

You can then do stuff like this in your View:

@this.Html.TextBoxFor(
    model => model.Name,
    p => p.Id = 7,
    p => p.Class = "my-class")

This gives you strong typing and intellisense for input properties, which you could customise for each extension method by adding properties to an appropriate MvcInputBuilder subclass.