IEnumerable Property can't return the value - asp.net-mvc

Question

I have ViewModel
public class Magazine_ViewModel
{
public int MagId { get; set; }
public string MagNo { get; set; }
public IEnumerable<Titles_ViewModel> Titles { get; set; }
}
public class Titles_ViewModel
{
public int TitleId { get; set; }
public string TitleName { get; set; }
public int pos { get; set; }
}
in Controller i do like this
var viewModel = new Magazine_ViewModel
{
Titles = numberTitles
.Select(c => new Titles_ViewModel
{
TitleId = c.TitleId,
TitleName = c.Title.TitleText,
pos=c.position
}).ToList()
};
viewModel.MagNo = magazine.MagNo.ToString();
viewModel.MagId = magazine.Id;
when i check viewModel.Titles has n records which is right.
now in the view part
<div class="editor-label">
#Html.LabelFor(model => model.MagNo)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.MagNo)
</div>
<div class="editor-field">
#Html.ListBox("wholeTitles")
<input type="button" name="add" id="add" value="add" onclick="addValue()" /><input type="button" name="remove" id="remove" value="remove" onclick="removeValue()"/>
#Html.ListBoxFor(model => model.Titles, new SelectList(Model.Titles, "TitleId", "TitleName"))
</div>
<p>
<input type="submit" value="Save" />
</p>
I add new Titles from first ListBox(wholeTitles) to second ListBox(Titles). Now the submit button is press and i want to add the new Titles to the database.
This is what i do in Post Action
[HttpPost]
public ActionResult EditTitle(Magazine_ViewModel magazineViewModel)
{
if (ModelState.IsValid)
{
var magazineTitles = new Magazine
{
Id = magazineViewModel.MagId,
NumberTitles = new List<NumberTitle>()
};
foreach (var numberTitle in magazineViewModel.Titles)
{
NumberTitle newNumberTitle = new NumberTitle();
newNumberTitle.MagazineId = magazineViewModel.MagId;
newNumberTitle.TitleId = numberTitle.TitleId;
newNumberTitle.position = 0;
unitOfWork.NumberTitleRepository.Insert(newNumberTitle);
}
}
return View();
}
but magazineViewModel.Titles shows null, I don't know what should I check to see why it is null value.

Answer 1

Your values not get posted back to the server. Use below in your View. This should post the titles back to the Server within the same ViewModel
for (var i = 0; i < Model.Titles.Count(); i++)
{
#Html.HiddenFor(m => m.Titles[i].TitleId)
#Html.HiddenFor(m => m.Titles[i].TitleName)
}