Checkbox Extension

Checkbox Extension.cs

namespace UI.Helpers
{
  using System;
	using System.Collections.Generic;
	using System.Linq.Expressions;
	using System.Text;
	using System.Web.Mvc;
	using System.Web.Mvc.Html;
	using System.Web.Routing;

	public static class FormHtmlHelperExtensions
	{

public static MvcHtmlString CheckBoxListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper,
  	                                                               Expression<Func<TModel, TProperty[]>> expression,
		                                                               MultiSelectList multiSelectList,
		                                                               object htmlAttributes = null, string prefix = "")
		{
			//Derive property name for checkbox name
			MemberExpression body = expression.Body as MemberExpression;
			string propertyName = body.Member.Name;

			//Get currently select values from the ViewData model
			TProperty[] list = expression.Compile().Invoke(htmlHelper.ViewData.Model);

			//Convert selected value list to a List<string> for easy manipulation
			IList<string> selectedValues = new List<string>();

			if (list != null)
			{
				selectedValues = new List<TProperty>(list).ConvertAll(delegate(TProperty i) { return i.ToString(); });
			}

			//Create div
			TagBuilder divTag = new TagBuilder("div");
			divTag.MergeAttributes(new RouteValueDictionary(htmlAttributes), true);

			divTag.InnerHtml += String.Format("<div class=\"group multi-select-options\">");

			//Add checkboxes
			foreach (SelectListItem item in multiSelectList)
			{
				var item2 = item;
				var id = "multi-select-" + Guid.NewGuid().ToString();
				divTag.InnerHtml +=
					String.Format(
						"<div class=\"group field multi-select-option\"><input type=\"checkbox\" name=\"{4}{0}\" id=\"{0}_{1}_{5}\" " +
						"value=\"{1}\" {2} /><label for=\"{0}_{1}_{5}\">{3}</label></div>",
						propertyName,
						item.Value,
						selectedValues.Contains(item.Value) ? "checked=\"checked\"" : "",
						item.Text, prefix, id);
			}

			divTag.InnerHtml += String.Format("</div>");

			return MvcHtmlString.Create(divTag.ToString());
		}
	}   
}

usage.md

Razor

@Html.CheckBoxListFor(model => model.SelectedSomethingIds, Model.Somethings, new { @class = "required" })

View Model

public MultiSelectList Somethings { get; set; } public int[] SelectedSomethingIds { get; set; }

Controller

// _listService.GetSomethings() returns IEnumerable

model.Somethings = new MultiSelectList(_listService.GetSomethings(), "Id", "Name");