MVC Model is null on post

Question

My viewmodel works fine on GET, but on post it is null and I cannot understand why. Any help would be greatly appreciated. The Quiz-post doesn't do much at this stage, I need to access the posted model before I can finish the method. The repository.GetAllQuestionsList() returns a list of QuizViewModel

ViewModel

    public class QuizViewModel {
    public int Id { get; set; }
    public int QuestionId { get; set; } 
    public string QuestionText { get; set; } 
    public int QuestionNbr { get; set; } 
    public int CurrentQuestion { get; set; } 
    public int TotalNbrOfQuestions { get; set; } 
    public List<Answer> Answers { get; set; } 
}

Controller

    public ActionResult Quiz() {
        var getAllQuestions = repository.GetAllQuestionsList();
        var model = getAllQuestions.Where(c => c.QuestionNbr == 1);
        Session["CurrentQ"] = 1;
        return View(model);
    }

    [HttpPost]
    public ActionResult Quiz(IEnumerable<Models.QuizViewModel> model) {

        int question = Convert.ToInt32(Session["CurrentQ"]);
        string str = Request.Params["btnSubmit"];
        if (str == "Next Question") {
             question++;
            Session["CurrentQ"] = question;
        }
        if (str == "Prev Question") {
             question--;
            Session["CurrentQ"] = question;
        }

       return View(model);
    }

View

@model IEnumerable<Quiz.Models.QuizViewModel>

@{
Layout = null;
}

<!DOCTYPE html>

<html>
<head>
<meta name="viewport" content="width=device-width"/>
<title>Quiz</title>
</head>

<body>
<p>
    @Html.ActionLink("Create New", "Create")
</p>
@using (Html.BeginForm()) {
<table class="table">
    <tr>
        <th>
            @Html.DisplayNameFor(model => model.QuestionText)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.QuestionNbr)
        </th>
        <th>
            answer
        </th>
        <th></th>
    </tr>

    @foreach (var item in Model) {
        <tr>
            <td>
                @Html.DisplayFor(modelItem => item.QuestionText)
            </td>
            <td>
                @Html.DisplayFor(modelItem => item.QuestionNbr)
            </td>
            <td>
                @foreach (var ML in item.Answers) {
                    @Html.RadioButtonFor(model => item.Answers, ML.Id)
                    @Html.Label(ML.AnswerText)
                    <br/>
                }
            </td>
        </tr>
    }

</table>
<input type="submit" id="Submit1" name="btnSubmit" value="Prev Question"/>
<input type="submit" id="Submit2" name="btnSubmit" value="Next Question"/>
}
</body>

</html>

Your view code doesn't make sense. If your model is an `IEnumerable` then `model.QuestionText` shouldn't work (at all!) — Liam, Oct 28 '15 at 16:38
Possible duplicate of [Model Binding to a List MVC 4](http://stackoverflow.com/questions/15375800/model-binding-to-a-list-mvc-4) — Liam, Oct 29 '15 at 08:24

score 2 · Accepted Answer · answered Oct 28 '15 at 17:30

I dont't think your code will work ever as the name binding are not generated properly also @Html.DisplayNameFor(model => model.QuestionText) and @Html.DisplayNameFor(model => model.QuestionNbr) will throw exception as Model is of type IEnumerable. HttpPost binding works only if the name are input controls are generated appropriately in generated html when posted to server. I have corrected your code.Please refer the below

@{
Layout = null;
}

<!DOCTYPE html>

<html>
<head>
<meta name="viewport" content="width=device-width"/>
<title>Quiz</title>
</head>

<body>
<p>
    @Html.ActionLink("Create New", "Create")
</p>
@using (Html.BeginForm()) {
<table class="table">

       <tr>
          <th>
            @Html.DisplayNameFor(model => model[0].QuestionText)
          </th>
          <th>
            @Html.DisplayNameFor(model => model[0].QuestionNbr)
          </th>
          <th>
             answer
          </th>
           <th></th>
        </tr>
    @for (int index = 0; index > Model.Count; index++) {
        <tr>
            <td>
                @Html.DisplayFor(modelItem => modelItem[index].QuestionText)
            </td>
            <td>
                @Html.DisplayFor(modelItem => modelItem[index].QuestionNbr)
            </td>
            <td>
                @for (int jIndex = 0; jIndex < Model[index].Answers; jIndex++ ) {
                    @Html.RadioButtonFor(model => modelItem[index].Answers[jIndex].Answer, modelItem[index].Answers[jIndex].Id)
                    @Html.Label(modelItem[index].Answers[jIndex].AnswerText)
                    <br/>
                }
            </td>
        </tr>
    }

</table>
<input type="submit" id="Submit1" name="btnSubmit" value="Prev Question"/>
<input type="submit" id="Submit2" name="btnSubmit" value="Next Question"/>
}
</body>

</html>

score 1 · Answer 2 · answered Oct 28 '15 at 16:41

Ignoring the @Html.DisplayNameFor(model => model.QuestionText) which (as I said doesn't make sense). You just need to change you iterator so that it knows where in the array the item lives, i.e.

@for (int i = 0; i < Model.Count; i++) {
        <tr>
            <td>
                @Html.DisplayFor(modelItem => modelItem[i].QuestionText)
            </td>
            <td>
                @Html.DisplayFor(modelItem => modelItem[i].QuestionNbr)
            </td>
       ..... etc
}

foreach doesn't work very well in an MVC view because the HTML helper doesn't know where in the array it is and the names aren't built up correctly.

MVC Model is null on post

2 Answers2