#region 下拉列表

         /// <summary>

         /// 联动下拉列表

         /// </summary>

         /// <param name="htmlHelper">被扩展的HtmlHelper实例</param>

         /// <param name="expression">获取数据集合</param>

         /// <param name="level">显示多少级</param>

         /// <param name="defaultValue">TProperty类型的默认值（如string默认值为"")</param>

         /// <param name="rootItems">获取根级列表数据</param>

         /// <param name="getParentID">获取列表项的ParentID方法</param>

         /// <param name="getChildItems">获取子级列表数据集合方法</param>

         /// <param name="getChildSelectDataUrl">获取子级列表数据的远程地址</param>

         /// <returns>html代码</returns>

         public static MvcHtmlString LinkageDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, TProperty defaultValue, int level, Dictionary<TProperty, string> rootItems,Func<TProperty, TProperty> getParentID, Func<TProperty, Dictionary<TProperty, string>> getChildItems,string getChildSelectDataUrl,string optionLabel = "请选择")

         {

             ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);

             return LinkageDropDownList(htmlHelper, ExpressionHelper.GetExpressionText(expression), (TProperty)metadata.Model, defaultValue, level, rootItems, getParentID,getChildItems,getChildSelectDataUrl,optionLabel);

         }

         /// <summary>

         /// 联动下拉列表

         /// </summary>

         /// <param name="htmlHelper">被扩展的HtmlHelper实例</param>

         /// <param name="level">显示多少级</param>

         /// <param name="defaultValue">TProperty类型的默认值（如string默认值为"")</param>

         /// <param name="name">下拉列表表单项名</param>

         /// <param name="selectedValue">当前选中值</param>

         /// <param name="rootItems">获取根级列表数据</param>

         /// <param name="getParentId">获取列表项的ParentID方法</param>

         /// <param name="getChildItems">获取子级列表数据集合方法</param>

         /// <param name="getChildSelectDataUrl">获取子级列表数据的远程地址</param>

         /// <returns>html代码</returns>

         public static MvcHtmlString LinkageDropDownList<TProperty>(this HtmlHelper htmlHelper, string name, TProperty selectedValue,TProperty defaultValue, int level, Dictionary<TProperty, string> rootItems, Func<TProperty, TProperty> getParentId, Func<TProperty, Dictionary<TProperty, string>> getChildItems, string getChildSelectDataUrl, string optionLabel = "请选择")

         {

             string fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);

             //select data init

             Stack<Dictionary<TProperty, string>> stack = new Stack<Dictionary<TProperty, string>>();

             //如果有选中的值，则查找其所在列表前面的所有列表

             IList<TProperty> selectedValues = new List<TProperty>();

             if (selectedValue != null && !selectedValue.Equals(defaultValue))

             {

                 TProperty itemId = selectedValue;

                 TProperty parentItemId = getParentId(itemId);

                 while (!itemId.Equals(defaultValue) && !parentItemId.Equals(defaultValue))

                 {

                     stack.Push(getChildItems(parentItemId));

                     selectedValues.Add(itemId);

                     itemId = parentItemId;

                     parentItemId = getParentId(itemId);

                 }

                 if (rootItems.Count() > )

                 {

                     TProperty rootId = getParentId(rootItems.First().Key);

                     if (!itemId.Equals(rootId))

                     {

                         stack.Push(rootItems);

                         selectedValues.Add(itemId);

                     }

                 }

             }

             else

             {

                 TProperty rootItemID = rootItems.Select(n => n.Key).FirstOrDefault();

                 stack.Push(rootItems);

             }

             //生成标签

             TagBuilder containerBuilder = new TagBuilder("span");

             containerBuilder.MergeAttribute("plugin", "linkageDropDownList");

             var data = new Dictionary<string, object>();

             data.TryAdd("GetChildSelectDataUrl", getChildSelectDataUrl);

             data.TryAdd("ControlName", name);

             data.TryAdd("Level", level);

             data.TryAdd("OptionLabel", optionLabel);

             data.TryAdd("DefaultValue", defaultValue.ToString());

             containerBuilder.MergeAttribute("data", Json.Encode(data));

             int currentIndex = ;

             while (stack.Count > )

             {

                 Dictionary<TProperty, string> dictionary = stack.Pop();

                 IEnumerable<SelectListItem> selectList = dictionary.Select(n => new SelectListItem() { Selected = selectedValues.Contains(n.Key), Text = n.Value, Value = n.Key.ToString() });

                 containerBuilder.InnerHtml += "\r\n" + htmlHelper.DropDownList(string.Format("{0}_{1}", name, currentIndex), selectList,

                                 optionLabel, new { @class = "tn-dropdownlist" });

                 currentIndex++;

             }

             containerBuilder.InnerHtml += "\r\n" + htmlHelper.Hidden(name);

             return MvcHtmlString.Create(containerBuilder.ToString());

         }

         #endregion