MVC dynamic data passing to controller

Question

I am creating a MVC application. I am having a view with a form to fill, but it seems that controller does not get data that was entered (it is null when debugging).
My controller:

public ActionResult AddGroupsQty(AddGroupsQtyViewModel value)
{

    var model = new AddGroupsQtyViewModel();
    model.subject_id = value.subject_id;
    model.qty = value.qty;
    ClassDeclarationsDBEntities1 entities1=new ClassDeclarationsDBEntities1();
    var subj = entities1.Subjects
            .Where(b => b.class_id == model.subject_id)
            .FirstOrDefault();
    model.subject_name = subj.name;
    if (ModelState.IsValid)
    {
        int maxId = 0;
        int total = 0;

        total = entities1.Groups.Count();
        if (total == 0)
        {
            maxId = 0;
        }
        else
        {
            maxId = entities1.Groups.Max(u => u.group_id);

        }
        for (int i = 0; i < value.qty; i++)
        {
            var teacher = entities1.Users
            .Where(b => b.email.Replace(" ", String.Empty) == model.teacher_emails[i].Replace(" ", String.Empty))
            .FirstOrDefault();
            var group=new Models.Group(value.subject_id, maxId+1, model.group_names[i], teacher.user_id);
            entities1.Groups.Add(group);
            entities1.SaveChangesAsync();
        }
        return RedirectToAction("OperationSuccess", "Account");

    }
    return View(model);
}

My View model:

public class AddGroupsQtyViewModel
{
    public int qty { get; set; }
    public int subject_id { get; set; }
    public string subject_name { get; set; }
    [Required]
    [Display(Name = "Name of group")]
    public List<string> group_names { get; set; }
    [Required]
    [Display(Name = "Email of teacher")]
    public List<string> teacher_emails { get; set; }
}

and the View:

@using System.IdentityModel.Configuration
@using System.Web.UI.WebControls
@model ClassDeclarationsThsesis.Models.AddGroupsQtyViewModel

@{
    ViewBag.Title = "AddGroupsQty";
}

<h2>Add Groups to @Model.subject_name</h2>
@if (Model != null)
{


    using (Html.BeginForm("AddGroupsQty", "Account", new { qty = Model.qty, Model.subject_id }, FormMethod.Post, new { @class = "form-horizontal", role = "form", }))
    {
            @Html.AntiForgeryToken()
            <h4>Insert data</h4>
            <hr />
            <table>
                <tr>
                    <th>
                        @Html.ValidationSummary("", new { @class = "text-danger" })
                        <div class="form-group">
                            @Html.LabelFor(m => m.group_names, new { @class = "col-md-2 control-label" })
                        </div>
                    </th>
                    <th>
                        @Html.ValidationSummary("", new { @class = "text-danger" })
                        <div class="form-group">
                            @Html.LabelFor(m => m.teacher_emails, new { @class = "col-md-2 control-label" })
                        </div>
                    </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.group_names[i], new { @class = "form-control" })
                                </div>
                            </div>

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

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



                        </th>
                    </tr>
                }
            </table>

            <div class="form-group">
                <div class="col-md-offset-2 col-md-10">
                    <input type="submit" class="btn btn-default" value="Submit" />
                </div>
            </div>
                    }
                        }

The problem is that when running the application, filling the form and submitting by pressing the button, it throws a null exception in controller that both lists:

List teacher_emails

and:

List group_names

are null. I do not see any error in my form. How can I solve it?

Answer 1

model.teacher_emails and model.group_names are always null, because model is new.

 var model = new AddGroupsQtyViewModel();

Try using value.teacher_emails and value.group_names instead.

Also tidy that code up. A blank line after the variable declaration, and you would have spotted it yourself.