MVC RadioButtonFor How & What to POST back to Controller

Question

New new to C# and MVC, so apologies in advance for posting something which is probably obvious.I have looked at similar answers but still can't see how and what value in the RadioButtonFor should be used so that it can be POSTed back to the controller.

Controller

    [HttpPost]
    public ActionResult Score(ExamViewModel exam)
    { 
        const int AddCorrect = 1;

        var correct = from c in db.Answers
                      where c.ID == 1
                      select c.CorrectAnswer;


        if (ModelState.IsValid)
        {
            if (correct == exam.CorrectAnswer) 
            {

                ViewData["message"] = "Correct Answer!";

                return View("Results");
           }

            else
            {
                var feedback = from g in db.Questions
                               where g.ID == 1
                               select g.GrammarPoint;

                ViewData["message"] = "That's not the right answer.";
                 ViewData["feedback"] = feedback;

                return View("Results");
            }

        }

        return View("Results"); 

And the View

  @model AccessEsol.Models.ExamViewModel

@{
    ViewBag.Title = "TakeTest";
}

<h2>TakeTest</h2>

@using (Html.BeginForm()) {
@Html.AntiForgeryToken()
@Html.ValidationSummary(true)

<fieldset>


    <div class="display-label">
        <h3>Click the correct answer:</h3>
    </div>

    <div class="display-field">

        <strong>@Html.DisplayFor(model => model.Text.Text )</strong>
    </div>

    @Html.DisplayFor(model => model.Foil1.Foil1)
   @Html.RadioButtonFor(model =>model.Foil1, "Incorrect" ) 

    @Html.DisplayFor(model => model.Foil2.Foil2)   
    @Html.RadioButtonFor(model => model.Foil2, "Incorrect" )

   @Html.DisplayFor(model => model.Foil3.Foil3)
    @Html.RadioButtonFor(model => model.Foil3, "Incorrect")


    @Html.DisplayFor(model => model.CorrectAnswer.CorrectAnswer)
    @Html.RadioButtonFor(model => model.CorrectAnswer, "Correct")   

    <p>
        <input type="submit" value="Submit Answers" />
    </p>

</fieldset>
}

I also tried to pass a string from the CorrectAnswer into the Score Controller without success.Much appreciated if you can point to how can checked RadioButton value can be passed back to the Controller?

Answer 1

You should not have 3 different properties but instead a single one that will contain the answer. This will allow you to group the radio buttons and be able to select only one of them:

@model AccessEsol.Models.ExamViewModel

@{
    ViewBag.Title = "TakeTest";
}

<h2>TakeTest</h2>

@using (Html.BeginForm()) 
{
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)

    <fieldset>
        <div class="display-label">
            <h3>Click the correct answer:</h3>
        </div>

        <div class="display-field">
            <strong>@Html.DisplayFor(model => model.Text.Text)</strong>
        </div>

        @Html.DisplayFor(model => model.Foil1.Foil1)
        @Html.RadioButtonFor(model => model.Answer, "1") 

        @Html.DisplayFor(model => model.Foil2.Foil2)   
        @Html.RadioButtonFor(model => model.Answer, "2")

        @Html.DisplayFor(model => model.Foil3.Foil3)
        @Html.RadioButtonFor(model => model.Answer, "3")

        @Html.DisplayFor(model => model.CorrectAnswer.CorrectAnswer)
        @Html.RadioButtonFor(model => model.Answer, "4")

        <p>
            <input type="submit" value="Submit Answers" />
        </p>
    </fieldset>
}

and then in your controller action check if the Answer property value that is sent is the correct one for this question. As you can see from the view we have multiple answer for the question and the value is what will get sent to the server. Usually you will use the ID of the answer as value and on the server you can compare whether this is the correct answer for the question.