如何将项目添加到在ASP.net MVC的选择列表

业务场景是这样：项目中有查询字典表返回的是ienumerable，绑定到前台dropdownlist。需要在selectlist第一项加上“==请选择==”。

网上搜了，大概有7种方法：

1. 真的没有必要，除非你坚持的值为0做到这一点。该在HtmlHelper DropDownList的扩展允许您设置一个选项标签，显示了在选择一个空值的初始值.a个DropDownList的签名，有该选项的标签。

<%= Html.DropDownList( "DropDownValue",
      (IEnumerable<SelectListItem>)ViewData["Menu"],
      "-- Select One --" ) %>


2. 我得到这个通过填充一个SelectItemList，转换为一个列表，并在索引0添加一个值来工作。

List<SelectListItem> items = new SelectList(CurrentViewSetups, "SetupId", "SetupName", setupid).ToList(); 
items.Insert(0, (new SelectListItem { Text = "[None]", Value = "0" }));
ViewData["SetupsSelectList"] = items;


3. 

public static SelectList IndividualNamesOrAll(this SelectList Object)
   {
    MedicalVarianceViewsDataContext LinqCtx = new MedicalVarianceViewsDataContext();
    var IndividualsListBoxRaw =
        (
        from x in LinqCtx.ViewIndividualsNames //not correct need individual view!
        orderby x.FullName
        select x
        );
    List<SelectListItem> items = new SelectList
           (
            IndividualsListBoxRaw, "First_Hospital_Case_Nbr", "FullName"
           ).ToList();
    items.Insert(0, (new SelectListItem { Text = "All Individuals", Value = "0.0", Selected = true }));
    Object = new SelectList
       (
       items,"Value","Text"
       );
    return Object;
   }


4.

private SelectList AddFirstItem(SelectList list)
  {
   List<SelectListItem> _list = list.ToList();
   _list.Insert(0, new SelectListItem() { Value = "-1", Text = "This Is First Item" });
   return new SelectList((IEnumerable<SelectListItem>)_list, "Value", "Text");
  }

这应该做你需要的，只是发送您的选择列表 CodeGo.net，它会返回一个选择列表中的一个项目索引0 您可以将文字，值或项目，甚至索引你需要插入
5. 使用C#扩展方法

static public class SelectListHelper
{
 static public SelectList Add(this SelectList list, string text, string value = "", ListPosition listPosition = ListPosition.First)
 {
  if (string.IsNullOrEmpty(value))
  {
   value = text;
  }
  var listItems = list.ToList();
  var lp = (int)listPosition;
  switch (lp)
  {
   case -1:
    lp = list.Count();
    break;
   case -2:
    lp = list.Count() / 2;
    break;
   case -3:
    var random = new Random();
    lp = random.Next(0, list.Count());
    break;
  }
  listItems.Insert(lp, new SelectListItem { Value = value, Text = text });
  list = new SelectList(listItems, "Value", "Text");
  return list;
 }
 public enum ListPosition
 {
  First = 0,
  Last = -1,
  Middle = -2,
  Random = -3
 }
}

用法（由为例）：

var model = new VmRoutePicker
 {
  Routes =
  new SelectList(_dataSource.Routes.Select(r => r.RouteID).Distinct())
  };          
 model.Routes = model.Routes.Add("All", "All", SelectListHelper.ListPosition.Random);
//or
 model.Routes = model.Routes.Add("All");


6. 听起来可能不是很优雅，但这样做：

 var items = repository.func.ToList();
 items.Insert(0, new funcItem { ID = 0, TextValue = "[None]" });
 ViewBag.MyData = new SelectList(items);


7. 这是可能的。

//Create the select list item you want to add
SelectListItem selListItem = new SelectListItem() { Value = "null", Text = "Select One" };
//Create a list of select list items - this will be returned as your select list
List<SelectListItem> newList = new List<SelectListItem>();
//Add select list item to list of selectlistitems
newList.Add(selListItem);
//Return the list of selectlistitems as a selectlist
return new SelectList(newList, "Value", "Text", null);


8. 我不知道如果任何人有一个更好的选择...

<% if (Model.VariableName == "" || Model.VariableName== null) { %>
 <%= html.DropDpwnList("ListName", ((SelectList) ViewData["viewName"], "", 
  new{stlye=" "})%>
<% } else{ %>
<%= html.DropDpwnList("ListName", ((SelectList) ViewData["viewName"], 
  Model.VariableName, new{stlye=" "})%>
<% }>