Html.DropDownListの<option>の下にhtmlクラスタグを追加する

Question

Html.dropdownlistにHTMLクラスタグを追加する方法に関する回答を探しています。ここにコードがあります

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

Select要素の下にオプションのクラスを追加して、この連鎖selectを使用できるようにします。

<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");

Answer 1

これは、使用するDropDownListではなく、DropDownlistFor拡張メソッドに対して行いましたが、おそらく自分で理解できるでしょう。このようなものは主にMVCソースからのコピー/貼り付けです。ソースを見つけることができます こちら 。

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);
    }
}

Answer 2

@ john-landheerのソリューションの少し改善されたバージョンを次に示します。

改善されたもの：

• GetModelStateValue()の問題を修正
• DropDownList()拡張メソッドが追加されました

• 控えめな検証属性は、必要なようにレンダリングされます

  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);
          }
  
      }
  }
  

Answer 3

これは、ASP.NET MVCに組み込まれているDropDownListヘルパーでは不可能です。そのため、必要な場合は独自のヘルパーを作成する必要があります。 TagBuilderを使用してオプションを生成するASP.NET MVCのソースコードを見て、カスタム実装に属性を追加できます。別のよりエレガントなソリューションは、ビュー内のデータセットを手動でループし、個々のオプション要素を生成することです。

Answer 4

ここで最初に思い浮かぶのは、JQueryです。次のコードで簡単にこれを行うことができます：

$("#bla").find("option").addClass("poo");

Answer 5

Htmlを単に変更するラッパーを作成しました。

    public static MvcHtmlString DisableFirstItem(MvcHtmlString htmlString)
    {
        return new MvcHtmlString(
            htmlString.ToString()
            .Replace("<option value=\"Unknown\">", 
                     "<option disabled value=\"Unknown\">")
        );
    }

そして、このヘルパー関数でDropDownListForをラップしました：

        @Html.Raw(MyHtmlHelpers.DisableFirstItem(

          Html.DropDownListFor(m => m.Instrument,
            new SelectList(ReflectionHelpers.GenerateEnumDictionary<OrderInstrument>(true), "Key", "Value", Model.Instrument),
            new { @class = "form-control" })

        ))

必要に応じて、ヘルパー機能をより洗練させることができます。