ASP.NET MVC View pass null reference to controller

Question

Why when i click on <input type="submit" value="Transpose" /> it pass TableViewModel object in TransposeMatrix function where TableViewModel.Matrix=null. Why Matrix is null? What i missed when used @Html.HiddenFor(model => model.Matrix)?

TableViewModel:

namespace MvcApplication1.Models
{
    public class TableViewModel
    {
        public int Rows { get; set; }

        public int Columns { get; set; }

        public double[,] Matrix { get; set; }
    }
}

HomeController:

namespace MvcApplication1.Controllers
{
    public class HomeController : Controller
    {
        //
        // GET: /Home/
        public ActionResult Index()
        {
            return View();
        }

        public ActionResult MatrixSizeIndex()
        {
            return View();
        }

        public ActionResult SetMatrixSize(TableViewModel tableViewModel)
        {
            int rows = tableViewModel.Rows;
            int columns = tableViewModel.Columns;
            tableViewModel.Matrix = new double[rows, columns];
            Random rnd = new Random();
            for (int i = 0; i < rows; i++)
            {
                for (int j = 0; j < columns; j++)
                {
                    tableViewModel.Matrix[i, j] = rnd.Next(9);
                }
            }
            return View(tableViewModel);
        }

        public ActionResult TransposeMatrix(TableViewModel tableViewModel)
        {
            return View(tableViewModel);
        }    
    }
}

MatrixSizeIndex.cshtml

@model MvcApplication1.Models.TableViewModel

@{
    ViewBag.Title = "SetMatrixSize";
}

@using (Html.BeginForm("TransposeMatrix", "Home"))
{
    <table>
        @for (int row = 0; row < Model.Rows; row++)
        {
            <tr>
                @for (int column = 0; column < Model.Columns; column++)
                {
                    <td>@Model.Matrix[row, column]</td>
                }
            </tr>
        }
    </table>

    @Html.HiddenFor(model => model.Rows)
    @Html.HiddenFor(model => model.Columns)
    @Html.HiddenFor(model => model.Matrix)
    <input type="submit" value="Transpose" />
}

I have not tried binding and posting a 2D array. Can you show what gets rendered in the "hidden" element? I suspect there is either a problem with that binding or what it posts. — Theo
– Theo, Commented Jan 3, 2017 at 15:47
I haven't tried testing your code, but would it work if your view used an ienumerable<model> instead of a flat one? — nocturns2
– nocturns2, Commented Jan 3, 2017 at 16:58

Jelle Oosterbosch · Accepted Answer · 2017-01-03 16:04:57Z

2

You should do a hidden for every value in the matrix:

@for (int row = 0; row < Model.Rows; row++)
{
    @for (int column = 0; column < Model.Columns; column++)
    {
        @HiddenFor(model => model.Matrix[row, column])
    }
}

answered Jan 3, 2017 at 16:04

Jelle Oosterbosch

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Comments

Munikrishna · Accepted Answer · 2017-01-03 16:21:02Z

Please use below syntax In .cshtml file

    **Use FormExtensions.BeginForm Method (HtmlHelper, String, String, Object, FormMethod, Object)**

example 1 :

    @using (Html.BeginForm("Index", "Settings",  new { id = "test1" }, FormMethod.Post, null))
    {
      <input type="submit" name="SaveButton" value="Save" />
    }

example 2 :-

@using (Html.BeginForm("TransposeMatrix", "Home", FormMethod.Post, null))
{
    <table>
        @for (int row = 0; row < Model.Rows; row++)
        {
            <tr>
                @for (int column = 0; column < Model.Columns; column++)
                {
                    <td>@Model.Matrix[row, column]</td>
                }
            </tr>
        }
    </table>

    @Html.HiddenFor(model => model.Rows)
    @Html.HiddenFor(model => model.Columns)
    @Html.HiddenFor(model => model.Matrix)
    <input type="submit" value="Transpose" />
    You are using FormExtensions.BeginForm Method (HtmlHelper, String, String, FormMethod, Object), where object is for the HTML attributes to set for the element. Currently it is setting the id of the form tag.

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