编辑视图中的ASP MVC 3 DropDown列表

Question

嗨大家好用asp mvc，所以我在编辑视图中遇到DropDown问题：

The ViewData item that has the key 'ProvinciaID' is of type 'System.Int32' but must be of type 'IEnumerable<SelectListItem>'.

Provincia模型：

public class Provincia
    {
        public int ProvinciaID { get; set; }
        [DisplayName("Provincia")]
        [Required(ErrorMessage = "Provincia es requerida")]
        public string ProvinciaNombre { get; set; }
    }

Registro模型：

public class Registro
    {
        public int ID { get; set; }
        ....

        [DisplayName("Provincia")]
        [Required]
        public int ProvinciaID { get; set; }
        public List<Provincia> rProvincia { get; set; }
        ....
}

控制器

public ActionResult Edit(int id)
        {
            Registro registro = db.Registros.Find(id);

            ViewBag.provincias = new SelectList(db.Provincias, "ProvinciaID", "ProvinciaNombre", registro.ProvinciaID);            

            return View(registro);
        }

查看

<div class="editor-label">
            @Html.LabelFor(model => model.ProvinciaID)
        </div>
        <div class="editor-field">
            @Html.DropDownList("ProvinciaID", (IEnumerable<SelectListItem>)ViewData["provincias"]))
            @Html.ValidationMessageFor(model => model.ProvinciaID)
        </div>

有什么想法吗？

谢谢你们

Answer 1

问题是您在其他控制器操作中使用此编辑视图（您在问题中显示的视图），而此其他控制器操作未设置ViewBag.provincias。如果要使用此视图，则必须始终设置ViewBag.provincias。我想这个其他的控制器动作就是你要发布到表单的动作：

[HttpPost]
public ActionResult Edit(Registro registro)
{
    if (!ModelState.IsValid)
    {
        // I guess that here you are trying to redisplay the Edit view
        // but you forgot to set ViewBag.provincias as you did in the
        // GET Edit action and an exception is thrown because the Edit view
        // always expects ViewBag.provincias to be set

        // So set it before returning to the same view:

        ViewBag.provincias = new SelectList(db.Provincias, "ProvinciaID", "ProvinciaNombre", registro.ProvinciaID);

        return View(registro);
    }
    return RedirectToAction("Success");
}