CODEWITHSUNDEEP
asp.net-mvc-3
ServerMonkey
ServerMonkey

Reputation: 1154

DropDownListFor - Model Binding

My first MVC project and have ran into an issue which I hope someone can assist with.

Basically I have a DropDownListFor object which I want to populate with a list of available times for the user to pick from and store the selected item in an attribute for later consumption.

The below is producing a null value error so I'm missing something obvious, any help would be appreciated.

Here's what I have:

Controller:

private MyModelObject m_model = new MyModelObject();
public ActionResult Index()
{
    var AvailTimes = new SelectList(new[]
    {
        new {Value="00:00",Text="12:00 AM"},
        new {Value="00:30",Text="12:30 AM"},
        new {Value="01:00",Text="1:00 AM"},
        new {Value="22:30",Text="10:30 PM"},
        new {Value="23:00",Text="11:00 PM"},
        new {Value="23:30",Text="11:30 PM"},                 
    }); 
    return View(m_model);
}

Model:

public class MyModelObject
{
    public string StartTime { get; set; }
    public IEnumerable<SelectList> AvailTimes { get; set; }
}

View:

@Html.DropDownListFor(model => model.StartTime, 
                       new SelectList(model.AvailTimes, "Value", "Text"))

Upvotes: 3

Views: 12202

Answers (2)

Darin Dimitrov
Darin Dimitrov

Reputation: 1039538

Don't make your model a private variable to the controller. Each time a request is sent a new controller instance will be created so don't think that you will be able to reuse it between actions. Also you don't seem to be doing anything useful with the AvailTimes local variable that you declared in your action and it is subject to a fast garbage collection. Also your model is incorrect. The AvailTimes property must be an IEnumerable<SelectListItem> and not IEnumerable<SelectList>.

Let's start by fixing the view model first:

public class MyModelObject
{
    public string StartTime { get; set; }
    public IEnumerable<SelectListItem> AvailTimes { get; set; }
}

then the controller action which will feed the view model:

public ActionResult Index()
{
    var model = MyModelObject
    {
        AvailTimes = new[]
        {
            new SelectListItem { Value = "00:00", Text = "12:00 AM" },
            new SelectListItem { Value = "00:30", Text = "12:30 AM" },
            new SelectListItem { Value = "01:00", Text = "1:00 AM" },
            new SelectListItem { Value = "22:30", Text = "10:30 PM" },
            new SelectListItem { Value = "23:00", Text = "11:00 PM" },
            new SelectListItem { Value = "23:30", Text = "11:30 PM" },                 
         } 
    };
    return View(model);
}

and finally the strongly typed view:

@model MyModelObject
@Html.DropDownListFor(x => x.StartTime, Model.AvailTimes)

You also have the possibility to assign those available hours in your view model directly:

public class MyModelObject
{
    public string StartTime { get; set; }
    public IEnumerable<SelectListItem> AvailTimes 
    { 
        get
        {
            return new[]
            {
                new SelectListItem { Value = "00:00", Text = "12:00 AM" },
                new SelectListItem { Value = "00:30", Text = "12:30 AM" },
                new SelectListItem { Value = "01:00", Text = "1:00 AM" },
                new SelectListItem { Value = "22:30", Text = "10:30 PM" },
                new SelectListItem { Value = "23:00", Text = "11:00 PM" },
                new SelectListItem { Value = "23:30", Text = "11:30 PM" },                 
             }; 
        }
    }
}

Now your controller action could become:

public ActionResult Index()
{
    var model = MyModelObject();
    return View(model);
}

and the view obviously stays unchanged.

Upvotes: 12

devdigital
devdigital

Reputation: 34369

The value of Model.AvailTimes is never assigned, therefore is null by default.

Upvotes: 0

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