Error after i httppost - know dropdown after i have click button

Question

when I click on my body and take a value, click the button, so when clicked on it so make this one mistake.

I've tried many things now drop down and inside behind my code but it still gives me the same error. I try the bebug and see how it happens.

The ViewData item that has the key 'SelectedOpgaveValue' is of type 'System.String' but must be of type 'IEnumerable'.

Line 48:                 
Line 49:         <div class="form-group">
Line 50:             @Html.DropDownListFor(x => x.SelectedOpgaveValue, Model.OpgaveValueList, new
Line 51:                 {
Line 52:                     @class = "form-control"

My controller:

        [MvcApplication.SessionExpire]
    [HttpGet]
    public ActionResult Index()
    {
        DataLinqDB db = new DataLinqDB();
        OpgaverPage model = new OpgaverPage();

        var random = new Random();
        var antalopgaver = db.Questions.Count();
        var number = random.Next(antalopgaver);

        //henter en random spørgsmål.
        var A = db.Questions.Where(i => i.fk_Categories == 1).Skip(number).Take(1).FirstOrDefault();
        model.Overskift = A.title;
        model.HiddenId = A.id;

        //Henter alle de svar muligheder man har til den id som man få fra A
        List<Question_Answer> QA = db.Question_Answers.Where(i => i.fk_Question == A.id).ToList();

        //dropdown her
        List<SelectListItem> items = new List<SelectListItem>();
        foreach (var item in QA.ToList())
        {
            items.Add(new SelectListItem() { Text = item.text, Value = item.id.ToString() });
        }

        //seleced dropdown
        model.OpgaveValueList = new SelectList(items, "Value", "Text");

        return View(model);
    }

    [MvcApplication.SessionExpire]
    [HttpPost]
    public ActionResult index(OpgaverPage opgavervalue)
    {
        DataLinqDB db = new DataLinqDB();
        if (ModelState.IsValid)
        {
            var opgaver = db.Question_Answers.FirstOrDefault(i => i.fk_Question == opgavervalue.HiddenId);
            if (opgaver != null)
            {
                if (opgavervalue.SelectedOpgaveValue.ToString() == opgaver.id.ToString() && opgaver.er_svaret == true)
                {
                    PointHelper.Point.PointInsert("opgaver");
                }
                else
                {
                    //error
                    ModelState.AddModelError("", "Desværre dit svar forkert");
                }
            }
            else
            {
                return RedirectToAction("index");
            }
        }
        return View(opgavervalue);
    }

Model:

public class OpgaverPage
{
    public string Overskift { get; set; }
    public int HiddenId { get; set; }
    [Display(Name ="Spørgsmål")]
    public string Svar { get; set; }
    public List<Question_Answer> QuestionList { get; set; }
    public IEnumerable<SelectListItem> OpgaveValueList { get; set; }
    public string SelectedOpgaveValue { get; set; }
}

index.cshtml

<p>@Model.Overskift</p>
@using (Html.BeginForm("index", "Opgaver"))
{
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)
    @Html.HiddenFor(i => i.HiddenId)              
    <div class="form-group">
        // Error is here!!
        @Html.DropDownListFor(x => x.SelectedOpgaveValue, Model.OpgaveValueList, new { @class = "form-control" })
    </div>
    <button type="submit" class="btn btn-effect-ripple btn-success"><i class="fa fa-check"></i> Tjek mit svar</button>
}

It because in the POST method you return the view but have not reassigned the SelectList - i.e. model.OpgaveValueList = new SelectList(items, "Value", "Text"); as you did in the GET method — user3559349
– user3559349, Commented Dec 2, 2015 at 22:11

score 0 · Accepted Answer · 2015-12-02 22:45:35Z

0

The error occurs because when you return the view in the POST method, the value of OpgaveValueList is null (and the DropDownListFor() method falls back to the overload that expects the first parameter to be IEnumerable. You need to reassign the value of OpgaveValueList before you return the view as you did in the GET method.

Note also there is no point in the extra overhead of geerating a second IEnumerable<SelectListItem> (which is what SelectList is) from the first one. Your code can simply be

List<SelectListItem> items = new List<SelectListItem>();
foreach (var item in QA.ToList())
{
    items.Add(new SelectListItem() { Text = item.text, Value = item.id.ToString() });
}
model.OpgaveValueList = items;
return View(model);

Or even simpler

model.OpgaveValueList = QA.Select(x => new SelectListItem
{
  Text = x.text,
  Value = x.id.ToString()
};

To keep things DRY, I suggest you create a private method

private void ConfigureViewmodel(OpgaverPage model)
{
  model.OpgaveValueList = db.Question_Answers.Where(i => i.fk_Question == A.id.Select(x => new SelectListItem
  {
    Text = x.text,
    Value = x.id.ToString()
  };
}

and then in both the GET and POST methods call it before returning the view

ConfigureViewmodel(model);
return View(model);

edited Dec 2, 2015 at 22:45

answered Dec 2, 2015 at 22:22

user3559349

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6 Comments

Jesper Petersen Over a year ago

I have tried to do as you write and explain but it tells me still the same error unfortunately. :(

user3559349 Over a year ago

It does not. You must have made another error as well. Are you sure you have added that code in the POST method?

Jesper Petersen Over a year ago

Where in the POST do you want the pregnant ??

user3559349 Over a year ago

I have updated the answer. And what do you mean want the pregnant?

Jesper Petersen Over a year ago

you write like this, Are you sure you have added that code in the POST method? then I think just where would you like to want me to throw it into the post

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