Question

我一直在阅读StackOverflow但是没有什么能真正帮助我解决这个问题。我正在研究一个位置模型，其中包含来自其他几个模型的字段的SelectLists，但每次我尝试保存时都会收到错误：

“System.Web.Mvc.dll中发生了'System.InvalidOperationException'类型的异常，但未在用户代码中处理

附加信息：没有类型为“IEnumerable”的ViewData项具有“CompanyID”键。“

以下是我认为的相关代码：

查看/位置/ Create.cshtml

<div class="form-group">
    <label class="control-label col-md-2">Company</label>
    <div class="col-md-10">
        @Html.DropDownList("CompanyID", (SelectList)ViewBag.AllCompanies, new { @class = "form-control" })
    </div>
</div>

以下是我的控制器的相关代码：

控制器/ PositionController.cs

        // GET: /Position/Create
        public ActionResult Create()
        {
            //create query to find all committees
            var query = from m in db.Majors
                        orderby m.Major
                        select m;
            //execute query and store in list
            List<Majors> allMajors = query.ToList();

            //convert list to select list format needed for HTML
            SelectList allMajorsList = new SelectList(allMajors, "MajorID", "Major");

            ViewBag.AllMajors = allMajorsList;

            //create query to find all committees
            var query2 = from c in db.Companies
                        orderby c.CompanyName
                        select c;
            //execute query and store in list
            List<Company> allCompanies = query2.ToList();

            //convert list to select list format needed for HTML
            SelectList allCompaniesList = new SelectList(allCompanies, "CompanyID", "CompanyName");

            ViewBag.AllCompanies = allCompaniesList;

            //create query to find all committees
            var query3 = from i in db.Industries
                         orderby i.IndustryName
                         select i;
            //execute query and store in list
            List<Industry> allIndustries = query3.ToList();

            //convert list to select list format needed for HTML
            SelectList allIndustriesList = new SelectList(allIndustries, "IndustryID", "IndustryName");

            ViewBag.AllIndustries = allIndustriesList;

            return View();
        }

    // POST: /Position/Create
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see http://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include="PositionID,PositionTitle,PositionType,PositionLocation,PositionDeadline,PositionDescription")] Position position, int[] SelectedMajors, Int32 CompanyID, Int32 IndustryID)
    {
        //find selected committee
        Company SelectedCompany = db.Companies.Find(CompanyID);
        Industry SelectedIndustry = db.Industries.Find(IndustryID);

        //associate committee with event
        position.PositionCompany = SelectedCompany;
        position.PositionIndustry = SelectedIndustry;

        if (ModelState.IsValid)
        {

            //if there are majors to add, add them
            if (SelectedMajors != null)
            {
                foreach (int MajorId in SelectedMajors)
                {
                    Majors majorToAdd = db.Majors.Find(MajorId);
                    position.ApplicableMajors.Add(majorToAdd);
                }
            }

            db.Positions.Add(position);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

        return View(position);
    }

我似乎无法弄清楚我做错了什么。任何帮助将不胜感激！

Answer 1

您的问题是settings.py很可能是错误的...当您从POST返回View时，您没有重置ViewBag值。

如果ViewBag值为null，则视图将在ViewData中查找与属性名称匹配的内容，这就是您收到该错误的原因。如果您对[HttpGet]操作中的所有代码进行注释并只返回View，则会出现相同的错误。

您应该尝试将所有这些代码移动到私有空间中。

if (ModelState.IsValid)

然后将您的GET操作更改为

private void LoadViewBag() 
{
        //create query to find all committees
        var query = from m in db.Majors
                    orderby m.Major
                    select m;
        //execute query and store in list
        List<Majors> allMajors = query.ToList();

        //convert list to select list format needed for HTML
        SelectList allMajorsList = new SelectList(allMajors, "MajorID", "Major");

        ViewBag.AllMajors = allMajorsList;

        //create query to find all committees
        var query2 = from c in db.Companies
                    orderby c.CompanyName
                    select c;
        //execute query and store in list
        List<Company> allCompanies = query2.ToList();

        //convert list to select list format needed for HTML
        SelectList allCompaniesList = new SelectList(allCompanies, "CompanyID", "CompanyName");

        ViewBag.AllCompanies = allCompaniesList;

        //create query to find all committees
        var query3 = from i in db.Industries
                     orderby i.IndustryName
                     select i;
        //execute query and store in list
        List<Industry> allIndustries = query3.ToList();

        //convert list to select list format needed for HTML
        SelectList allIndustriesList = new SelectList(allIndustries, "IndustryID", "IndustryName");

        ViewBag.AllIndustries = allIndustriesList;
}

然后将您的发布操作更改为

    // GET: /Position/Create
    public ActionResult Create()
    {

        LoadViewBag();
        return View();
    }

没有类型为“IEnumerable <selectlistitem>”的ViewData项具有密钥“CompanyID”

1 个答案: