ASP.NET MVC 下拉列表未在渲染时选择值？ [复制]

Question

在模型的帮助下从控制器发送一个选择列表来查看=>

如下图=>

ViewBag.vendor_heading = new SelectList(db.Vendors , "heading", "heading", course.vendor_heading);
return View(course);

问题在于选择列表未显示我从控制器发送的选定值。 在视图中=> 在上面我只是输出以检查供应商名称并显示 =>look 它显示供应商名称 ORACLE，但在下拉列表中选择的值是 CISCO。为什么会发生这种情况。

我的查看代码=>

@model Course

<div>
    @Html.LabelFor(model => model.vendor_heading, "vendor Name", new { @class = "control-label" })
    @Html.DisplayFor(model => model.vendor_heading)
</div>
<div>
     @Html.LabelFor(model => model.vendor_heading, "vendor Name", new { @class = "control-label" })
     @Html.DropDownList("vendor_heading", (SelectList)ViewBag.vendor_heading, new { @class = "form-control input-lg", @style = "min-height:45px;" })
     @Html.ValidationMessageFor(model => model.vendor_heading, null, new { @class = "text-danger" })
 </div>

和我的模型=>

    public class Course
{
    [MaxLength(700, ErrorMessage = "The Max Length For Heading Is 700 Character!")]
    public string vendor_heading { get; set; }
    /// <summary>
    /// //////////
    /// </summary>
    [Key]
    [Required(AllowEmptyStrings = false, ErrorMessage = "Course Name Is Required!")]
    [MaxLength(700, ErrorMessage = "The Max Length For Course Name Is 700 Character!")]
    [Display(Name = "Course Name")]
    public string name { get; set; }
    /// <summary>
    /// //////////
    /// </summary>
    [Required(AllowEmptyStrings = false, ErrorMessage = "Course Code Is Required!")]
    [MaxLength(200, ErrorMessage = "The Max Length For Course Code Is 200 Character!")]
    [Display(Name = "Course Code")]
    public string code { get; set; }
    /// <summary>
    /// //////////
    /// </summary>
    [Required(AllowEmptyStrings = false, ErrorMessage = "Picture Is Required!")]
    [MaxLength(1000, ErrorMessage = "The Max Length For Pic Path Is 1000 Character!")]
    [Display(Name = "Pic")]
    public string pic_path { get; set; }
    /// <summary>
    /// /////////
    /// </summary>
    [Required(ErrorMessage = "Adding date Is Required!")]
    [DataType(DataType.Date, ErrorMessage = "Invalid Date!")]
    [Display(Name = "Adding Date")]
    public DateTime adding_date { get; set; }
    /// <summary>
    /// /////////
    /// </summary>
    [MaxLength(5000, ErrorMessage = "The Max Length For Course Details Is 5000 Character!")]
    [Display(Name = "Course Details")]
    public string details { get; set; }

    //relationship With  other tables-------
    [ForeignKey("vendor_heading")]
    public Vendor Vendor { get; set; }
    public List<Batche> Batches { get; set; }
}

我已经给了我完整的模型课，有很多不必要的员工。请忽略。

请告诉我或建议我做错了什么以及在哪里？

Answer 1

尝试像下面的代码定义下拉列表

 @Html.DropDownList("vendor_heading", (SelectList)ViewBag.vendor_heading,htmlAttributes: new { @class = "form-control input-lg", @style = "min-height:45px;" })