Html.ActionLink extension

Question

I am trying to extend the Html.ActionLink as I want to add a custom meta data for a shared component (in this case a modal).

My aim is to further extend the LinkExtensions class within .Net MVC which will add a value to the html class attribute and add a custom data attribute resulting in the following:

<a href="/Controller/Action/id" class="show-in-modal style1 style2" data-title="Modal title">Link</a>

The helper will look similar to the MVC method:

public static MvcHtmlString ModalLink(this HtmlHelper htmlHelper, string title, string linkText, string actionName, string controllerName, object routeValues, object htmlAttributes)
{
    // Add 'show-in-modal' class here
    // Add 'data-title' attribute here

    return htmlHelper.ActionLink(linkText, actionName, controllerName, routeValues, htmlAttributes);
}

@Html.ModalLink("Modal title", "Link", "action", "controller", new { id = "id" }, new { @class = "style1 style2" });

This issue I am having is I cannot easily modify the htmlAttributes object to add my class name and data attribute, which makes sense as this is a read only anonymous object.

Is there a way I can easily apply the required values/meta data without having to rip everything apart with reflection and put back together again?

I noticed MVC has overloads which accepts html attributes in the form of an IDictionary<string, object>, is there an extension method which converts anonymous types to a modifiable dictionary?

All i get within searching is how to use the Html.ActionLink() method.

Answer 1

The function you are looking for is:

HtmlHelper.AnonymousObjectToHtmlAttributes()

https://msdn.microsoft.com/en-us/library/system.web.mvc.htmlhelper.anonymousobjecttohtmlattributes(v=vs.118).aspx

Here is one version of the ModalLink Extension:

public static MvcHtmlString ModalLink(this HtmlHelper htmlHelper, string title, string linkText, string actionName, string controllerName, object routeValues, object htmlAttributes)
{
  // Add 'show-in-modal' class here
  // Add 'data-title' attribute here

  var htmlAttr = HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes);

  const string classKey = "class";
  const string titleKey = "data-title";

  const string classToAdd = "show-in-modal";
  if (htmlAttr.ContainsKey(classKey) == true)
  {
    htmlAttr[classKey] += " " + classToAdd;
  }
  else
  {
    htmlAttr.Add(classKey, classToAdd);
  }

  if (htmlAttr.ContainsKey(titleKey) == true)
  {
    htmlAttr[titleKey] = title;
  }
  else
  {
    htmlAttr.Add(titleKey, title);
  }

  return htmlHelper.ActionLink(linkText, actionName, controllerName, new RouteValueDictionary(routeValues), htmlAttr);
}

Answer 2

I made a helper class for exactly this sort of situation a while back. This is a basic cut down version of it. I left the XML comments in for one of the methods because it's a bit confusing otherwise.

HtmlAttributes.cs

/// <copyright file="HtmlAttributes.cs"><author username="Octopoid">Chris Bellini</author></copyright>

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Text;
using System.Web.Mvc;

public class HtmlAttributes : Dictionary<string, object>
{
    public HtmlAttributes()
        : base()
    {
    }

    public HtmlAttributes(object anonymousAttributes)
        : base(HtmlHelper.AnonymousObjectToHtmlAttributes(anonymousAttributes))
    {
    }

    public HtmlAttributes(IDictionary<string, object> attributes)
        : base(attributes)
    {
    }

    public void Add(object anonymousAttributes)
    {
        this.Add(HtmlHelper.AnonymousObjectToHtmlAttributes(anonymousAttributes));
    }

    public void Add(IDictionary<string, object> attributes)
    {
        foreach (var attribute in attributes)
        {
            this.Add(attribute.Key, attribute.Value);
        }
    }

    public void AddCssClass(string cssClass)
    {
        if (cssClass == null) { throw new ArgumentNullException("cssClass"); }

        string key = "class";
        if (this.ContainsKey(key))
        {
            string currentValue;
            if (this.TryGetString(key, out currentValue))
            {
                this[key] = currentValue + " " + cssClass;
                return;
            }
        }

        this[key] = cssClass;
    }

    public void Remove(object anonymousAttributes)
    {
        this.Remove(HtmlHelper.AnonymousObjectToHtmlAttributes(anonymousAttributes));
    }

    /// <summary>
    /// Removes the value with the specified key from the <see cref="System.Collections.Generic.Dictionary<TKey,TValue>"/>.
    /// This method hides the base implementation, then calls it explicity.
    /// This is required to prevent the this.Remove(object) method catching base.Remove(string) calls.
    /// </summary>
    /// <param name="key">The key of the element to remove.</param>
    /// <returns>
    /// true if the element is successfully found and removed; otherwise, false.
    /// This method returns false if key is not found in the System.Collections.Generic.Dictionary<TKey,TValue>.
    /// </returns>
    /// <exception cref="System.ArgumentNullException">key is null.</exception>
    public new bool Remove(string key)
    {
        return base.Remove(key);
    }

    public void Remove(IDictionary<string, object> attributes)
    {
        foreach (var attribute in attributes)
        {
            this.Remove(attribute.Key);
        }
    }

    public MvcHtmlString ToMvcHtmlString()
    {
        return new MvcHtmlString(this.ToString());
    }

    public override string ToString()
    {
        StringBuilder output = new StringBuilder();

        foreach (var item in this)
        {
            output.Append(string.Format("{0}=\"{1}\" ", item.Key.Replace('_', '-'), item.Value.ToString()));
        }

        return output.ToString().Trim();
    }

    public bool TryGetString(string key, out string value)
    {
        object obj;
        if (this.TryGetValue(key, out obj))
        {
            value = obj.ToString();
            return true;
        }
        value = default(string);
        return false;
    }
}

In your case, inside your helper method, you'd do this:

HtmlAttributes finalAttributes = new HtmlAttributes(htmlAttributes);
finalAttributes.Add("data_title", "title");
finalAttributes.AddCssClass("show-in-modal");

Note, you can add (or remove) them together on mass if needed too:

finalAttributes.Add(new { data_title = "title", id = "id", data_extra = "extra" });

You can then just pass in finalAttributes as normal, as it extends Dictionary<string, object>.

This is also helpful when you're making your own custom HTML control renderers, as you can use the attributes.ToMvcHtmlString() method to render out the attributes into HTML.