如果你不想使用jquery，那么你可以使用javascript：-

@Html.DropDownList("Sortby", new SelectListItem[] 
{ 
     new SelectListItem() { Text = "Newest to Oldest", Value = "0" }, 
     new SelectListItem() { Text = "Oldest to Newest", Value = "1" }},
     new { @onchange="callChangefunc(this.value)" 
});

<script>
    function callChangefunc(val){
        window.location.href = "/Controller/ActionMethod?value=" + val;
    }
</script>

你能做到的

@Html.DropDownList("Sortby", new SelectListItem[] { new SelectListItem() 
  { 

       Text = "Newest to Oldest", Value = "0" }, new SelectListItem() { Text = "Oldest to Newest", Value = "1" } , new
       {
           onchange = @"form.submit();"
       }
})

如果要将值传递给操作方法，可以尝试这样做。

@Html.DropDownList("Sortby", new SelectListItem[] { new SelectListItem() { Text = "Newest to Oldest", Value = "0" }, new SelectListItem() { Text = "Oldest to Newest", Value = "1" }},new { onchange = "document.location.href = '/ControllerName/ActionName?id=' + this.options[this.selectedIndex].value;" })

如果没有参数传递，则删除查询字符串。

试试这个：

@Html.DropDownList("Sortby", new SelectListItem[] { new SelectListItem() 
{ Text = "Newest to Oldest", Value = "0" }, new SelectListItem() 
{ Text = "Oldest to Newest", Value = "1" }},
new { onchange = "document.location.href = '/ControllerName/ActionName?id=' + this.options[this.selectedIndex].value;" })

首先你需要给予你的下拉onchange事件;

@Html.DropDownList("ddl_reportId", new SelectList(ViewBag.ddl_reportName, "ddl_reportId", "ddl_reportName"), "Raporu seçin", new { @class = "form-control", @onchange = "getVal()" })

然后在脚本部分你必须这样调用它。

function getVal() {
    var selectedVal = document.getElementById("ddl_reportId").value;
    console.log(selectedVal)};

如果您有列表视图，则可以执行以下操作：
1.定义选择列表：

@{
   var Acciones = new SelectList(new[]
   {
  new SelectListItem { Text = "Modificar", Value = 
   Url.Action("Edit", "Countries")},
  new SelectListItem { Text = "Detallar", Value = 
  Url.Action("Details", "Countries") },
  new SelectListItem { Text = "Eliminar", Value = 
  Url.Action("Delete", "Countries") },
 }, "Value", "Text");
}

1.使用定义的SelectList，为每条记录创建一个不同的id（记住每个元素的id在视图中必须是唯一的），最后调用onchange事件的javascript函数（在示例url和record key中包含参数）：

@Html.DropDownList("ddAcciones", Acciones, "Acciones", new { id = 
item.CountryID, @onchange = "RealizarAccion(this.value ,id)" })

1. onchange函数可以是：

@section Scripts {
<script src="~/Scripts/jquery-1.10.2.min.js"></script>
<script src="~/Scripts/jquery.unobtrusive-ajax.js"></script>

<script type="text/javascript">

function RealizarAccion(accion, country)
{

    var url = accion + '/' + country;
    if (url != null && url != '') {
        window.location.href = url ;
    }
}
</script>

@Scripts.Render("~/bundles/jqueryval")
}

如果您想在更改事件时调用Javascript函数，请尝试以下操作：@Html.DropDownList（“项目ID”，模型.项目，“选择项目”，新建字典〈字符串，对象〉{ {“类”，“选择2”}，{“onchange”，“onProjectSelect（）”} }）

function onProjectSelect() {
    //write your business logic..
}

字符串