MVC view data passing

Question

I am making my MVC application. My view PickGroupForHomework is redirected to by

return RedirectToAction("PickGroupForHomework", "Account", new { subject_id = id, qty=model.qty });  

Of course subject_id and qty are parameters of PickGroupForHomeworkViewModel. The controller looks like this:

public ActionResult PickGroupForHomework(PickGroupForHomeworkViewModel model)
{
    ClassDeclarationsDBEntities2 entities = new ClassDeclarationsDBEntities2();
    model.groups = entities.Groups.ToList();
    model.users = entities.Users.ToList();
    int id = model.subject_id;
    var subj = entities.Subjects
            .Where(b => b.class_id == model.subject_id)
            .FirstOrDefault();
    if (subj != null)
    {
        model.subject_name = subj.name;
    }
    if (ModelState.IsValid)
    {
        DateTime myDate = DateTime.ParseExact(model.deadline+ " "+model.time, "yyyy-MM-dd HH:mm",
                               System.Globalization.CultureInfo.InvariantCulture);
        ClassDeclarationsDBEntities2 entities2 = new ClassDeclarationsDBEntities2();
        int total = entities2.Tasks.Count();

        for (int i=0;i<model.task_names.Count;i++)
        {
            ClassDeclarationsDBEntities2 entities3 = new ClassDeclarationsDBEntities2();
            int maxid;
            if (total == 0)
            {
                maxid = 0;
            }
            else {
                maxid = entities3.Tasks.Max(u => u.task_id);
            }

            var task = new Models.Task(model.task_names[i], model.subject_id, myDate, model.points[i], maxid + 1);
            entities3.Tasks.Add(task);
            entities3.SaveChangesAsync();
        }
        return RedirectToAction("OperationSuccess", "Account");
    }
    else
    {
        return View(model);
    }
    return View(model);

}

At first, everything loads correctly with correct URL including data passed from previous view. The form I am displaying now includes validation. If a user makes mistake in form, which indicades ModelState.IsValid=false, the window is reloaded. But I do not know why it is reloaded without data passed from previous window: subject_id and qty. What am I doing wrong?
EDIT:

View:   @model ClassDeclarationsThsesis.Models.PickGroupForHomeworkViewModel

@{
    ViewBag.Title = "Pick Group For Homework"; }

<h2>Setting homework for @Model.subject_name</h2>

@foreach (var user in Model.users) {
    if (user.email.Replace(" ", String.Empty) == HttpContext.Current.User.Identity.Name)
    {
        if (user.user_type.Replace(" ", String.Empty) == 2.ToString()|| user.user_type.Replace(" ", String.Empty) == 3.ToString())
        {
            using (Html.BeginForm("PickGroupForHomework", "Account", FormMethod.Post, new { @class = "form-horizontal", enctype = "multipart/form-data" })) {
                @Html.AntiForgeryToken()
                <hr />
                <div class="form-group">
                    @Html.LabelFor(model => model.deadline, htmlAttributes: new { @class = "control-label col-md-2" })
                    <div class="col-md-10">
                        @Html.EditorFor(model => model.deadline, new { htmlAttributes = new { @class = "form-control" } })
                        @Html.ValidationMessageFor(model => model.deadline, "", new { @class = "text-danger" })
                    </div>
                </div>
                <div class="form-group">
                    @Html.LabelFor(model => model.time, htmlAttributes: new { @class = "control-label col-md-2" })
                    <div class="col-md-10">
                        @Html.EditorFor(model => model.time, new { htmlAttributes = new { @class = "form-control" } })
                        @Html.ValidationMessageFor(model => model.deadline, "", new { @class = "text-danger" })
                    </div>
                </div>
                <div class="form-group">
                    @Html.LabelFor(m => m.file, new { @class = "col-md-2 control-label" })
                    <div class="col-md-10">
                        <div class="editor-field">

                            <input type="file" name="file" />
                        </div>
                    </div>
                </div>
                <div class="form-group">

                    <table>
                        <tr>
                            <th>
                                Name of task
                            </th>
                            <th>
                                Points
                            </th>
                        </tr>

                        @for (int i = 0; i < Model.qty; i++)
                        {
                            <tr>
                                <th>
                                    <div class="form-group">
                                        <div class="col-md-10">

                                            @Html.TextBoxFor(m => m.task_names[i], new { @class = "form-control" })
                                        </div>
                                    </div>

                                </th>
                                <th>
                                    <div class="form-group">
                                        <div class="col-md-10">

                                            @Html.TextBoxFor(m => m.points[i], new { @class = "form-control" })
                                        </div>
                                    </div>
                                </th>
                            </tr>
                        }

                    </table>
                    </div>
                    <div class="form-group">
                        <div class="col-md-offset-2 col-md-10">
                            <input type="submit" class="btn btn-default" value="Submit" />
                        </div>
                    </div>
                    }
                    }
                    if (user.user_type.Replace(" ", String.Empty) == 1.ToString() )
                    {
                    <p>You do not have enough permissions to enter this page. Contact the administrator.</p>
                    }

                    }
                    }

Answer 1

Your problem is subject_id is not in your form, so when you post back the form it sends 0 value to the server.

you need to add a field inside form , you can add a Text or hidden field

@Html.HiddenFor(m => m.subject_id)