Adding html class tag under <option> in Html.DropDownList

I've been looking for answers on how to add an HTML class tag on my html.dropdownlist. here is the code

<%: Html.DropDownList("PackageId", new SelectList(ViewData["Packages"] as IEnumerable, "PackageId", "Name", Model.PackageId))%>

I want to add classes for options under the select element so that I can use this chained select :

<select id="category">
  <option value="1">One</option>
  <option value="2">Two</option>
</select>
<select id="package">
  <option value="1" class="1">One - package1</option>
  <option value="2" class="1">One - package2</option>
  <option value="3" class="2">Two - package1</option>
  <option value="4" class="2">Two - package2</option>
</select>

$("#series").chained("#mark");

Solution 1:

I've done this for the DropDownlistFor extension method, not the DropDownList you use, but you can probably figure that out yourself. This stuff is mostly copy/paste from the MVC sources. You can find the sources here.

public class ExtendedSelectListItem : SelectListItem
{
    public object htmlAttributes { get; set; }
}

public static partial class HtmlHelperExtensions
{
    public static MvcHtmlString ExtendedDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<ExtendedSelectListItem> selectList, string optionLabel, object htmlAttributes)
    {
        return SelectInternal(htmlHelper, optionLabel, ExpressionHelper.GetExpressionText(expression), selectList, false /* allowMultiple */, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
    }

    private static MvcHtmlString SelectInternal(this HtmlHelper htmlHelper, string optionLabel, string name, IEnumerable<ExtendedSelectListItem> selectList, bool allowMultiple, IDictionary<string, object> htmlAttributes)
    {
        string fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
        if (String.IsNullOrEmpty(fullName))
            throw new ArgumentException("No name");

        if (selectList == null)
            throw new ArgumentException("No selectlist");

        object defaultValue = (allowMultiple) ? GetModelStateValue(htmlHelper, fullName, typeof(string[])) : GetModelStateValue(htmlHelper, fullName, typeof(string));

        // If we haven't already used ViewData to get the entire list of items then we need to
        // use the ViewData-supplied value before using the parameter-supplied value.
        if (defaultValue == null)
            defaultValue = htmlHelper.ViewData.Eval(fullName);

        if (defaultValue != null)
        {
            IEnumerable defaultValues = (allowMultiple) ? defaultValue as IEnumerable : new[] { defaultValue };
            IEnumerable<string> values = from object value in defaultValues select Convert.ToString(value, CultureInfo.CurrentCulture);
            HashSet<string> selectedValues = new HashSet<string>(values, StringComparer.OrdinalIgnoreCase);
            List<ExtendedSelectListItem> newSelectList = new List<ExtendedSelectListItem>();

            foreach (ExtendedSelectListItem item in selectList)
            {
                item.Selected = (item.Value != null) ? selectedValues.Contains(item.Value) : selectedValues.Contains(item.Text);
                newSelectList.Add(item);
            }
            selectList = newSelectList;
        }

        // Convert each ListItem to an <option> tag
        StringBuilder listItemBuilder = new StringBuilder();

        // Make optionLabel the first item that gets rendered.
        if (optionLabel != null)
            listItemBuilder.Append(ListItemToOption(new ExtendedSelectListItem() { Text = optionLabel, Value = String.Empty, Selected = false }));

        foreach (ExtendedSelectListItem item in selectList)
        {
            listItemBuilder.Append(ListItemToOption(item));
        }

        TagBuilder tagBuilder = new TagBuilder("select")
        {
            InnerHtml = listItemBuilder.ToString()
        };
        tagBuilder.MergeAttributes(htmlAttributes);
        tagBuilder.MergeAttribute("name", fullName, true /* replaceExisting */);
        tagBuilder.GenerateId(fullName);
        if (allowMultiple)
            tagBuilder.MergeAttribute("multiple", "multiple");

        // If there are any errors for a named field, we add the css attribute.
        ModelState modelState;
        if (htmlHelper.ViewData.ModelState.TryGetValue(fullName, out modelState))
        {
            if (modelState.Errors.Count > 0)
            {
                tagBuilder.AddCssClass(HtmlHelper.ValidationInputCssClassName);
            }
        }

        tagBuilder.MergeAttributes(htmlHelper.GetUnobtrusiveValidationAttributes(name));

        return MvcHtmlString.Create(tagBuilder.ToString(TagRenderMode.Normal));
    }

    internal static string ListItemToOption(ExtendedSelectListItem item)
    {
        TagBuilder builder = new TagBuilder("option")
        {
            InnerHtml = HttpUtility.HtmlEncode(item.Text)
        };
        if (item.Value != null)
        {
            builder.Attributes["value"] = item.Value;
        }
        if (item.Selected)
        {
            builder.Attributes["selected"] = "selected";
        }
        builder.MergeAttributes(HtmlHelper.AnonymousObjectToHtmlAttributes(item.htmlAttributes));
        return builder.ToString(TagRenderMode.Normal);
    }
}

Solution 2:

Here's a little improved version of @john-landheer's solution.

Things improved:

  • problem with GetModelStateValue() fixed
  • DropDownList() extension method added
  • unobtrusive validation attributes will be rendered just like they should

    using System;
    using System.Collections;
    using System.Collections.Generic;
    using System.Globalization;
    using System.Linq;
    using System.Linq.Expressions;
    using System.Text;
    using System.Web;
    using System.Web.Mvc;
    
    namespace App.Infrastructure.Helpers
    {
        public class ExtendedSelectListItem : SelectListItem
        {
            public object HtmlAttributes { get; set; }
        }
    
        public static class ExtendedSelectExtensions
        {
            internal static object GetModelStateValue(this HtmlHelper htmlHelper, string key, Type destinationType)
            {
                System.Web.Mvc.ModelState modelState;
                if (htmlHelper.ViewData.ModelState.TryGetValue(key, out modelState))
                {
                    if (modelState.Value != null)
                    {
                        return modelState.Value.ConvertTo(destinationType, null /* culture */);
                    }
                }
                return null;
            }
    
            public static MvcHtmlString ExtendedDropDownList(this HtmlHelper htmlHelper, string name, IEnumerable<ExtendedSelectListItem> selectList)
            {
                return ExtendedDropDownList(htmlHelper, name, selectList, (string)null, (IDictionary<string, object>)null);
            }
    
            public static MvcHtmlString ExtendedDropDownList(this HtmlHelper htmlHelper, string name, IEnumerable<ExtendedSelectListItem> selectList, string optionLabel, IDictionary<string, object> htmlAttributes)
            {
                return ExtendedDropDownListHelper(htmlHelper, null, name, selectList, optionLabel, htmlAttributes);
            }
    
            public static MvcHtmlString ExtendedDropDownListHelper(this HtmlHelper htmlHelper, ModelMetadata metadata, string expression, IEnumerable<ExtendedSelectListItem> selectList, string optionLabel, IDictionary<string, object> htmlAttributes)
            {
                return SelectInternal(htmlHelper, metadata, optionLabel, expression, selectList, false, htmlAttributes);
            }
    
            public static MvcHtmlString ExtendedDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper,
                Expression<Func<TModel, TProperty>> expression, IEnumerable<ExtendedSelectListItem> selectList,
                string optionLabel, object htmlAttributes)
            {
                if (expression == null)
                    throw new ArgumentNullException("expression");
                ModelMetadata metadata = ModelMetadata.FromLambdaExpression<TModel, TProperty>(expression, htmlHelper.ViewData);
                return SelectInternal(htmlHelper, metadata, optionLabel, ExpressionHelper.GetExpressionText(expression), selectList,
                    false /* allowMultiple */, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
            }
    
            private static MvcHtmlString SelectInternal(this HtmlHelper htmlHelper, ModelMetadata metadata, string optionLabel, string name,
                IEnumerable<ExtendedSelectListItem> selectList, bool allowMultiple,
                IDictionary<string, object> htmlAttributes)
            {
                string fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
                if (String.IsNullOrEmpty(fullName))
                    throw new ArgumentException("No name");
    
                if (selectList == null)
                    throw new ArgumentException("No selectlist");
    
                object defaultValue = (allowMultiple)
                    ? htmlHelper.GetModelStateValue(fullName, typeof(string[]))
                    : htmlHelper.GetModelStateValue(fullName, typeof(string));
    
                // If we haven't already used ViewData to get the entire list of items then we need to
                // use the ViewData-supplied value before using the parameter-supplied value.
                if (defaultValue == null)
                    defaultValue = htmlHelper.ViewData.Eval(fullName);
    
                if (defaultValue != null)
                {
                    IEnumerable defaultValues = (allowMultiple) ? defaultValue as IEnumerable : new[] { defaultValue };
                    IEnumerable<string> values = from object value in defaultValues
                                                 select Convert.ToString(value, CultureInfo.CurrentCulture);
                    HashSet<string> selectedValues = new HashSet<string>(values, StringComparer.OrdinalIgnoreCase);
                    List<ExtendedSelectListItem> newSelectList = new List<ExtendedSelectListItem>();
    
                    foreach (ExtendedSelectListItem item in selectList)
                    {
                        item.Selected = (item.Value != null)
                            ? selectedValues.Contains(item.Value)
                            : selectedValues.Contains(item.Text);
                        newSelectList.Add(item);
                    }
                    selectList = newSelectList;
                }
    
                // Convert each ListItem to an <option> tag
                StringBuilder listItemBuilder = new StringBuilder();
    
                // Make optionLabel the first item that gets rendered.
                if (optionLabel != null)
                    listItemBuilder.Append(
                        ListItemToOption(new ExtendedSelectListItem()
                        {
                            Text = optionLabel,
                            Value = String.Empty,
                            Selected = false
                        }));
    
                foreach (ExtendedSelectListItem item in selectList)
                {
                    listItemBuilder.Append(ListItemToOption(item));
                }
    
                TagBuilder tagBuilder = new TagBuilder("select")
                {
                    InnerHtml = listItemBuilder.ToString()
                };
                tagBuilder.MergeAttributes(htmlAttributes);
                tagBuilder.MergeAttribute("name", fullName, true /* replaceExisting */);
                tagBuilder.GenerateId(fullName);
                if (allowMultiple)
                    tagBuilder.MergeAttribute("multiple", "multiple");
    
                // If there are any errors for a named field, we add the css attribute.
                System.Web.Mvc.ModelState modelState;
                if (htmlHelper.ViewData.ModelState.TryGetValue(fullName, out modelState))
                {
                    if (modelState.Errors.Count > 0)
                    {
                        tagBuilder.AddCssClass(HtmlHelper.ValidationInputCssClassName);
                    }
                }
    
                tagBuilder.MergeAttributes(htmlHelper.GetUnobtrusiveValidationAttributes(fullName, metadata));
    
                return MvcHtmlString.Create(tagBuilder.ToString(TagRenderMode.Normal));
            }
    
            internal static string ListItemToOption(ExtendedSelectListItem item)
            {
                TagBuilder builder = new TagBuilder("option")
                {
                    InnerHtml = HttpUtility.HtmlEncode(item.Text)
                };
                if (item.Value != null)
                {
                    builder.Attributes["value"] = item.Value;
                }
                if (item.Selected)
                {
                    builder.Attributes["selected"] = "selected";
                }
                builder.MergeAttributes(HtmlHelper.AnonymousObjectToHtmlAttributes(item.HtmlAttributes));
                return builder.ToString(TagRenderMode.Normal);
            }
    
        }
    }