Jquery 在DropDownList中自动选择所选项目

我在一个partialview里有一个下拉列表

 <div class="col-md-12">
     Referre To: @Html.DropDownListFor(m => m.SenderPosition_Id, ViewBag.senderPositionsList as SelectList, "--Select--", new { @class = "form-control" })
 </div>

此Dropdownlistfor在控制器中填充如下：

 List<ReferrableUsersViewModel> senderPositionsList = new List<ReferrableUsersViewModel>();       
 using (WebECartableEntities dc = new WebECartableEntities())
 {                          
    senderPositionsList = dc.Positions.Where(m => m.usr_Id == User.Identity.Name).Select(x => new ReferrableUsersViewModel
                {
                    SenderPosition_Id = x.ID,
                    Name_Position = x.Title
                }
                ).Distinct().OrderBy(m => m.Name_Position).ToList();


    ViewBag.senderPositionsList = new SelectList(senderPositionsList, "SenderPosition_Id", "Name_Position");
 }

我想如果DropdownlistFor有一个项目，它会被自动选择，但是如果它有多个项目，让用户选择它。

---

如何在MVC中做到这一点？

在控制器操作中，您可以检查集合的计数是否为1。将模型对象的SenderPosition\u Id设置为如下所示：

if(senderPositionsList.Count == 1)
{
     model.SenderPosition_Id = senderPositionsList.First().ID;
}
......
......
return View(model);