如何在mvc中获取dropdownlist选择的值

Question

我想在控制器中获取所选的下拉列表值。

它出现以下错误

  

没有类型为'IEnumerable＆lt; SelectListItem＆gt;'的ViewData项它有关键'studentid'

控制器代码

[HttpGet]
public ActionResult CallSqlScalarFuction()
{
    IList<int> StudentIDs = db.Students.Select(x => x.ID).ToList();
    ViewBag.studentid = StudentIDs.Select(x => new SelectListItem()
    {
        Text = x.ToString(),
        Value = x.ToString()
     });
     return View();
 }

[HttpPost]
public ActionResult CallSqlScalarFuction(int studentid)
{
    string sql = @"Select dbo.GetStudentNameById(@p0) as FullName";
    var studentFullName = db.Database.SqlQuery<string>(sql, studentid).ToList();
    ViewBag.studentFullName = studentFullName[0].ToString();
    return View();
}

CallSqlScalarFuction.cshtml

@using (Html.BeginForm("CallSqlScalarFuction", "Students",FormMethod.Post,null))
{
    @Html.Label("Please select StudentID:")
    @Html.DropDownList("studentid", (IEnumerable<SelectListItem>)ViewBag.studentid)
    <input type="submit" value="submit" class="btn btn-primary" />
}