Ytukyg

I have a dropdownlist, after submitting there is an error http://prntscr.com/lnagi8

This is the View

 @Html.DropDownListFor(m => m.SelectedAgrBall, Model.agrBall)

    <input type="submit" value="save" />

and this is Controller (Post)

[HttpPost]

public ActionResult Main(string Years, string Periods, Organisations m)

{

    string s = m.SelectedAgrBall;

    int ss = int.Parse(s);

    string t = Years;

    string b = Periods;

    return View();

}

What should i do?
Controller

public ActionResult Main()

    {

        aspregistrationEntities1 obj = new aspregistrationEntities1();



        List<agrBal> aggrBad = obj.agrBals.ToList();

        List<agrBReceiv> aggrRec = obj.agrBReceivs.ToList();



        SortedSet<string> org = new SortedSet<string>();

        List<SelectListItem> items = new List<SelectListItem>();

        Dictionary<int, string> orgNames = new Dictionary<int, string>();



        foreach (agrBal tmp in aggrBad)

        {

            org.Add(tmp.ORG.ToString());

        }

        foreach(agrBReceiv tmp in aggrRec)

        {

            orgNames.Add(int.Parse(tmp.PBS.ToString()), tmp.KBO_RU.ToString());

        }



        //Drop organisations in dropdownlist

        var types = new List<SelectListItem>();

        foreach (string tmp in org)

        {

            string s = tmp+" - "+orgNames[int.Parse(tmp)];

            SelectListItem item1 = new SelectListItem() { Text = s, Value = tmp.ToString() };

            items.Add(item1);

        }



        Organisations m = new Organisations() {

             agrBall= items

        };

        return View(m);

    }

Model

{

public class Organisations

{

    public List<SelectListItem> agrBall { get; set; }

    public string SelectedAgrBall { get; set; }

}

}

You return View without model on HttpPost action so null reference exception occurs because you're using Model object in Main.cshtml

You should pass the model object to view.

(I think) if your model is Organizations m like that

[HttpPost]

    public ActionResult Main(string Years, string Periods, Organisations m)

    {

        string s = m.SelectedAgrBall;

        int ss = int.Parse(s);

        string t = Years;

        string b = Periods;

        return View(m);

    } 

Followed furkanhb and then modified the model/post method to allow for reloading of the page with a pre-selected value

public class Organisations

{

    public List<SelectListItem> agrBall { get; set; }

    public SelectListItem SelectedAgrBall { get; set; }

}



[HttpPost]

public ActionResult Main(string Years, string Periods, Organisations m)

{

    string s = m.SelectedAgrBall.Value;

    int ss = int.Parse(s);

    string t = Years;

    string b = Periods;

    return View(m);

}