DropDownListFor的种种纠结（禁止转载）

严重禁止转载，好多爬虫软件为了浏览到处抓东西，真缺德

具有键“CorpType”的 ViewData 项属于类型“System.Int64”,但它必须属于类型“IEnumerable<SelectListItem>"

先吐槽，不是不依赖微软的东西，是我对微软的类库实在有种排斥感，有些东西错了又找不到原因，这个问题就找了5个小时

网上硬是没有解决办法，因为技术总监的缘故就得照着做，无奈~~~~~~

问题如下：

  public  class CorpModel
    {
        [Required]
        [Display(Name = "公司名称")]
        public string CorpName { get; set; }
        [Required]
        [Display(Name = "公司类型")]
        public long CorpType { get; set; }
 }

 public ActionResult AddCorporation()
        {
             var temp = dropDownListService.InitCorpTypeDropDownList11();
             ViewData["Types"] = new SelectList(temp, "ID", "Name"); ;
             return View(corptype);
        }

   <div class="form-group">
            @Html.LabelFor(model => model.CorpType, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.DropDownListFor(u => u.CorpType,Model.CorpTypeList , "-- Select Contact --", new { @class = "form-control", required = "true" })
                @Html.ValidationMessageFor(model => (SelectList)ViewData["Types"], "", new { @class = "text-danger" })
            </div>
        </div>

 第一次调用的时候是没问题的

 [HttpPost]
        public ActionResult AddCorporation(CorpModel corp)
        {
            var currentUser = HttpContext.Session[Constants.USER_KEY] as USP.Models.POCO.User;
       
            if (ModelState.IsValid)
            {
                AjaxResult result = sysCorpBll.AddCorporation(corp.CorpName, corp.CorpType, currentUser.SysCorp.ID);
                if (result.flag)
                {
                    return RedirectToAction("Corporation", "Corp");
                }
            }
            var temp = dropDownListService.InitCorpTypeDropDownList11();
            ViewData["Types"] = new SelectList(temp, "ID", "Name"); ;

            return View("AddCorporation", corp);
        }

 第二次就报上面异常了

最终的解决方案

再viewmodel中增加

public IEnumerable<SelectListItem> CorpTypeList { get; set; }

    public  class CorpModel
    {
        [Required]
        [Display(Name = "公司名称")]
        public string CorpName { get; set; }
        [Required]
        [Display(Name = "公司类型")]
        public long CorpType { get; set; }

        public IEnumerable<SelectListItem> CorpTypeList { get; set; }
    }

  [HttpGet]
        public ActionResult AddCorporation()
        {
            //var temp = dropDownListService.InitCorpTypeDropDownList11();

            //ViewData["Types"] = new SelectList(temp, "ID", "Name"); ;
            var temp = dropDownListService.InitCorpTypeDropDownList11();
            CorpModel corptype = new CorpModel();
            corptype.CorpTypeList = new SelectList(temp, "ID", "Name");
            return View(corptype);
        }

        [HttpPost]
        public ActionResult AddCorporation(CorpModel corp)
        {
            var currentUser = HttpContext.Session[Constants.USER_KEY] as USP.Models.POCO.User;
       
            if (ModelState.IsValid)
            {
                AjaxResult result = sysCorpBll.AddCorporation(corp.CorpName, corp.CorpType, currentUser.SysCorp.ID);
                if (result.flag)
                {
                    return RedirectToAction("Corporation", "Corp");
                }
            }
            var temp = dropDownListService.InitCorpTypeDropDownList11();
            corp.CorpTypeList= new SelectList(temp, "ID", "Name");

            return View("AddCorporation", corp);
        }

        <div class="form-group">
            @Html.LabelFor(model => model.CorpType, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.DropDownListFor(u => u.CorpType,Model.CorpTypeList , "-- Select Contact --", new { @class = "form-control", required = "true" })
                @Html.ValidationMessageFor(model => model.CorpType, "", new { @class = "text-danger" })
            </div>
        </div>

 这样就可以避免这种问题了。。。

在前边用了一个Html.DropDownListFor方法渲染控件

结果报异常，用reflector跟了半天，结果调用了MVCForm的IDispose方法，我也是醉了

有一个页面用了同样的方法去调用，没问题，到这里就有了问题，我想了想因为是Dispose了顺便又调用了GC，所以页面要重新加载

所以在调用View的时候就得重新赋值给这里的return View("AddCorporation", corp);是没有DropDownList的数据，以至于报错