Why is my ViewModel empty on [HttpPost]? .NET MVC 3

Question

I'm trying my hardest to use ViewModels correctly in my web application, but I'm running into various problems. One of which, is if I set a breakpoint just after I post using a Create action, my viewModel hasn't stored any of my form values. I must be doing something wrong, but I've tried a few things. Including the code below, where I name the form items the same as the viewModel fields to see if that helps.

I'm also wondering what exactly properties in your viewmodel should represent. I've seen people use different things in blog posts and whatnot.

If the view is going to render a select list, I'm under the impression the viewmodel should hold an IEnumerable SelectListItem for this as below. Yet I've seen people use IEnumerable Entity instead, to represent the type the select list represents.

Can anybody shed some light on this for me? I scrapped my entire business logic last night so I could start a fresh and try and do it correctly.

My ViewModel:

public class ServerCreateViewModel
{
    public int Id { get; set; }

    // CompanyName represents a field in the Company model. I did this to see if
    // it would help with model binding. Beforehand it was Companies to represent the type. I've done the same for the rest of them, so I wont comment on this again.
    public IEnumerable<SelectListItem> CompanyName { get; set; }

    // Represents the Game model.
    public IEnumerable<SelectListItem> GameTitle { get; set; }

    //Represents the Location model, etc...
    public IEnumerable<SelectListItem> City { get; set; }
    public IEnumerable<SelectListItem> NumberOfPlayers { get; set; }
    public IEnumerable<SelectListItem> CurrencyAbbreviation { get; set; }
}

My Controller action:

    public ActionResult Create()
    {
        var viewModel = new ServerCreateViewModel();

        viewModel.CompanyName = new SelectList(_dataService.Companies.All(), "Id", "CompanyName");
        viewModel.GameTitle = new SelectList(_dataService.Games.All(), "Id", "GameTitle");
        viewModel.City = new SelectList(_dataService.Locations.All(), "Id", "City");
        viewModel.NumberOfPlayers = new SelectList(_dataService.ServerPlayers.All(), "Id", "NumberOfPlayers");

        return View(viewModel);
    } 

    [HttpPost]
    public ActionResult Create(FormCollection collection, ServerCreateViewModel viewModel)
    {
        try
        {      // I put a breakpoint in here to check the viewModel values.
               // If I dont pass the viewModel into the constructor, it doesnt exist.
               // When I do pass it in, its empty.
            return Content("Success");
        }
        catch
        {
            return Content("Fail");
        }
    }

My View:

@model GameserverCompare.ViewModels.Server.ServerCreateViewModel


@using (Html.BeginForm())
{
@Html.ValidationSummary(true)
<fieldset>
    <legend>Server</legend>
    @Html.HiddenFor(m => m.Id)
     <div class="editor-label">
        @Html.LabelFor(model => model.CompanyName)
    </div>
    <div class="editor-field">
        @Html.DropDownListFor(m => Model.CompanyName, Model.CompanyName)
        @Html.ValidationMessageFor(model => model.CompanyName)
    </div>
     <div class="editor-label">
        @Html.LabelFor(model => model.GameTitle)
    </div>
    <div class="editor-field">
        @Html.DropDownListFor(m => Model.GameTitle, Model.GameTitle)
        @Html.ValidationMessageFor(model => model.GameTitle)
    </div>
    <div class="editor-label">
        @Html.LabelFor(model => model.City)
    </div>
    <div class="editor-field">
        @Html.DropDownListFor(m => Model.City, Model.City)
        @Html.ValidationMessageFor(model => model.City)
    </div>
    <div class="editor-label">
        @Html.LabelFor(model => model.NumberOfPlayers)
    </div>
    <div class="editor-field">
        @Html.DropDownListFor(m => Model.NumberOfPlayers, Model.NumberOfPlayers)
        @Html.ValidationMessageFor(model => model.NumberOfPlayers)
    </div>
    <p>
        <input type="submit" value="Create" />
    </p>

</fieldset>
}

score 4 · Accepted Answer · answered Oct 22 '11 at 08:20

4

Since you're using SelectList properties in the form model, you will need to have a different model to represent the selected values in those lists:

public class ServerCreatePostbackModel
{
    public int Id { get; set; }

    // CompanyName represents a field in the Company model. 
    public string CompanyName { get; set; }

    // Represents the Game model.
    public string GameTitle { get; set; }

    //Represents the Location model, etc...
    public string City { get; set; }
    public int NumberOfPlayers { get; set; }
    public string CurrencyAbbreviation { get; set; }
}

Have your HttpPost action take one of these as its argument.

Oh, and be sure to use HiddenFor for the Id property, so it gets sent back with the other data.

answered Oct 22 '11 at 08:20

StriplingWarrior

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Thanks, but does this mean I will still have to get the values from the POST by using Request.Form to populate the ServerCreatePostViewModel? – Kiada Oct 22 '11 at 08:39
No, the properties of the ServerCreatePostbackModel should automatically be bound to the form values that are provided. You shouldn't have to access the form data directly. – StriplingWarrior Oct 22 '11 at 08:57
I think I get you, so the property types in my post back model have to be the same as the types my form will post. I.e, the drop down list will return a string value, hence the corresponding property should also be a string (even though in reality the string represents an int reference Id for say.. the company). So although the viewmodel will capture the string, I'll have to parse it into an int to find the correct company to reference (or game, or whatever). Thanks! – Kiada Oct 22 '11 at 09:06
Last comment, tested it and it works fine. Thanks for helping me understand! – Kiada Oct 22 '11 at 09:27
@CraigWhitley: Actually, if the property is an int, the model binder will be smart enough to convert it to an int automatically (for example, on the NumberOfPlayers in the code I posted). – StriplingWarrior Oct 22 '11 at 13:54

Why is my ViewModel empty on [HttpPost]? .NET MVC 3

1 Answers1