【发布时间】：2013-11-12 02:16:52
【问题描述】：
我从数据库中填充下拉列表，我想通过设置它们的“类”属性以红色显示某些元素。所以，我尝试了很多方法，后来我为 Dropdownlist 创建了一个自定义 HTML Helper。但这没有任何意义，虽然它似乎是添加了类属性，但这个参数不能从 Controller 传递给 Razor View。你能帮忙吗？
MyHelper.cs：
public static MvcHtmlString Custom_DropdownList(this HtmlHelper helper, string name, IEnumerable<SelectListItem> list, object htmlAttributes)
{
TagBuilder dropdown = new TagBuilder("select");
dropdown.Attributes.Add("name", name);
dropdown.Attributes.Add("id", name);
StringBuilder options = new StringBuilder();
foreach (var item in list)
{
options = options.Append("<option value='" + item.Value + "'>" + item.Text + "</option>");
}
dropdown.InnerHtml = options.ToString();
dropdown.MergeAttributes(new RouteValueDictionary(htmlAttributes));
return MvcHtmlString.Create(dropdown.ToString(TagRenderMode.Normal));
}
控制器：
private void PopulateMeetingsDropDownList(object selectedMeetings = null)
{
var meetingsQuery = repository.Meetings
.Join(repository.Cities, m => m.MeetingCityId, c => c.CityID,
(m, c) => new
{
CityID = c.CityID,
CityName = c.CityName,
MeetingDate = m.MeetingStartDate
}
)
.OrderBy(x => x.CityID)
.AsEnumerable()
.Select(
i => new
{
CityID = i.CityID,
Name = string.Format(
"{0} ({1:dd MMMM yyyy})",
i.CityName, i.MeetingDate),
Expired = i.MeetingDate < DateTime.UtcNow
}
).ToList();
var selectItems = new List<SelectListItem>(meetingsQuery.Count);
foreach (var record in meetingsQuery)
{
var item = new SelectListItem
{
Text = record.Name,
Value = record.Name
};
if (record.Expired)
{
item.Attributes.Add("class", "disabled"); //!!! Problem on this line
}
selectItems.Add(item);
}
ViewData["MeetingId"] = new SelectList(meetingsQuery, "CityID", "Name", selectedMeetings);
}
但在应用此方法后，我收到错误“'System.Web.Mvc.SelectListItem' 不包含 'Attributes' 的定义，并且没有扩展方法 'Attributes' 接受类型的第一个参数......”。所以，我认为我需要使用另一个属性或助手将类属性分配给自定义 racords（在 "if (record.Expired)" 行过滤记录没有问题）。
查看：
@Html.Custom_DropdownList("MeetingId", ViewData["MeetingId"] as SelectList, new { id = "meetingId"})
你能解释一下如何提供这个吗？提前致谢。
以下是修改后的代码，用于同时具备 Class 和 Disabled 属性：
更新的代码（用于 MyDropdownListFor）：
自定义 HTML 助手类：
public static class MyHelpers
{
public class MySelectItem : SelectListItem
{
public string Class { get; set; }
public string Disabled { get; set; }
}
public static MvcHtmlString MyDropdownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<MySelectItem> list, string optionLabel, object htmlAttributes)
{
return MyDropdownList(htmlHelper, ExpressionHelper.GetExpressionText(expression), list, optionLabel, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
}
public static MvcHtmlString MyDropdownList(this HtmlHelper htmlHelper, string name, IEnumerable<MySelectItem> list, string optionLabel, IDictionary<string, object> htmlAttributes)
{
TagBuilder dropdown = new TagBuilder("select");
dropdown.Attributes.Add("name", name);
dropdown.Attributes.Add("id", name);
StringBuilder options = new StringBuilder();
// Make optionLabel the first item that gets rendered.
if (optionLabel != null)
options = options.Append("<option value='" + String.Empty + "'>" + optionLabel + "</option>");
foreach (var item in list)
{
if(item.Disabled == "disabled")
options = options.Append("<option value='" + item.Value + "' class='" + item.Class + "' disabled='" + item.Disabled + "'>" + item.Text + "</option>");
else
options = options.Append("<option value='" + item.Value + "' class='" + item.Class + "'>" + item.Text + "</option>");
}
dropdown.InnerHtml = options.ToString();
dropdown.MergeAttributes(new RouteValueDictionary(htmlAttributes));
return MvcHtmlString.Create(dropdown.ToString(TagRenderMode.Normal));
}
}
控制器：
private void PopulateMeetingsDropDownList(object selectedMeetings = null)
{
var meetingsQuery = repository.Meetings
.Join(repository.Cities, m => m.MeetingCityId, c => c.CityID,
(m, c) => new
{
CityID = c.CityID,
CityName = c.CityName,
MeetingDate = m.MeetingStartDate
}
)
.OrderBy(x => x.CityID)
.AsEnumerable()
.Select(
i => new
{
Value = i.CityID.ToString(),
DisplayValue = string.Format(
"{0} ({1:dd MMMM yyyy})",
i.CityName, i.MeetingDate),
Expired = i.MeetingDate < DateTime.UtcNow
}
).ToList();
var selectItems = new List<MyHelpers.MySelectItem>(meetingsQuery.Count);
foreach (var record in meetingsQuery)
{
var item = new MyHelpers.MySelectItem
{
Text = record.DisplayValue,
Value = record.Value
};
if (record.Expired)
{
item.Class = "disabled";
item.Disabled = "disabled";
}
selectItems.Add(item);
}
ViewBag.MeetingData = selectItems;
}
查看：
<label>Meeting</label>
@Html.MyDropdownListFor(m => m.MeetingId, ViewBag.MeetingData as List<MyHelpers.MySelectItem>, "---- Select ----",
new { name = "meetingId", id = "meetingId"})
【问题讨论】：
-
这是一个静态列表，我认为该主题与我的问题无关。
-
最简单的方法是将 text 属性与 text 和 class 连接起来，例如 text#class，然后在 helper 中拆分它......从代码的角度来看这是不对的......但这件事不会更改您现有的代码....如果将来您想添加更多属性或乐趣，那么 Slavo 的答案是正确的...创建自定义的..
标签： asp.net asp.net-mvc attributes html-helper html-select