Can not understand why i am getting System.ArgumentNullException was unhandled by user code

Question

i have the following Action method:-

    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult AssignGroup(int SecurityRoleID, int[] selectedGroups, int[] currentGroups)
            {try
                {if (ModelState.IsValid)
                    {   repository.AssignGroupRole(SecurityRoleID, selectedGroups, currentGroups);
                        repository.Save();
                        if (!Request.IsAjaxRequest())
                        {
                            return RedirectToAction("AssignGroup", new { id = SecurityRoleID });
                        }
                        else if (Request.IsAjaxRequest())
                        {
                            ViewBag.Users = repository.populateAssignedGroupData(SecurityRoleID);
                            return PartialView("_AssignGroup", repository.FindAllRole(SecurityRoleID));
                        }}}

And the following Partial view:-

@using (Html.BeginForm("AssignGroup", "SecurityRole", FormMethod.Post))
{

<span class="b">There are Currently @Model.Groups.Count() Group/s</span>
<table class="table table-striped table-bordered bootstrap-datatable datatable">
 <thead>
<tr>     
<th> @Html.DisplayNameFor(model => model.Groups.SingleOrDefault().Name)</th>
        <th></th>
        </tr>

        </thead>
        <tbody> 
        <tr>
        @{
                        int cnt = 0;
                        List<TMS.ViewModels.GroupAssign> groups = ViewBag.Groups;

                        foreach (var group in groups.OrderBy(a=>a.Name)) {
                            if (cnt++ % 5 == 0) {
                                @:  </tr> <tr> 
                            }
                            @: <td> 
                                <input type="checkbox" 
                                       name="selectedGroups" 
                                       value="@group.GroupId" 
        @(Html.Raw(group.IsChecked ? "checked=\"checked\"" : "")) /> 
        @:  @group.Name
        @Html.Hidden("currentGroups", group.GroupId)
                            @:</td>
                        }
                        @: </tr>
         }


        </tbody> 


         @Html.HiddenFor(model => model.SecurityRoleID)
        @Html.AntiForgeryToken()

         </table>

        <input type="submit" value="Assign Groups" class="btn btn-primary"/>}

and the following repository methods:-

public List<GroupAssign> populateAssignedGroupData(int SecurityRoleID)
        {
            var allGroups = AllGroup();
            var securityRole = FindAllRole(SecurityRoleID);

            var roleGroups = securityRole.Groups.Select(a => a.Name);

            var viewModel = new List<GroupAssign>();
            foreach (var group in allGroups)
            {
                viewModel.Add(new GroupAssign
                {
                    GroupId = group.GroupID,
                    Name = group.Name,
                    IsChecked = roleGroups.Contains(group.Name, StringComparer.OrdinalIgnoreCase)
                });
            }
            return viewModel;
        }

public void AssignGroupRole(int id, int[] selectedGroups, int[] currentGroups)
        {
            var roleGroups = FindRole(id).Groups;

            var securityRole = FindAllRole(id);

            foreach (var group in roleGroups.ToList())
            {
                if (currentGroups != null)
                {
                    for (int c = 0; c < currentGroups.Count(); c++)
                    {
                        if (group.GroupID == currentGroups[c])
                        {

                            securityRole.Groups.Remove(group);} }} }


            if (selectedGroups != null)
            {
                for (int i = 0; i < selectedGroups.Count(); i++)
                {
                   Group r = new Group();
                   r.GroupID = selectedGroups[i];
                   securityRole.Groups.Add(r);}}}

But whne i click on the "Assign Groups" button inside the view i will get the following error on the code foreach (var group in groups.OrderBy(a=>a.Name)) insdie the partial view:-

ystem.ArgumentNullException was unhandled by user code
HResult=-2147467261 Message=Value cannot be null. Parameter name: source Source=System.Core ParamName=source StackTrace: at System.Linq.OrderedEnumerable2..ctor(IEnumerable1 source, Func2 keySelector, IComparer1 comparer, Boolean descending) at System.Linq.Enumerable.OrderBy[TSource,TKey](IEnumerable1 source, Func2 keySelector) at ASP._Page_Views_SecurityRole__AssignGroup_cshtml.Execute() in c:\Users\Administrator\Documents\Visual Studio 2012\Projects\TMS\TMS\Views\SecurityRole_AssignGroup.cshtml:line 56 at System.Web.WebPages.WebPageBase.ExecutePageHierarchy() at System.Web.Mvc.WebViewPage.ExecutePageHierarchy() at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) at System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance) at System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer) at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) at System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult) at System.Web.Mvc.ControllerActionInvoker.<>c_DisplayClass1a.b_17() at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation)
InnerException:

Ant P Ant P · Accepted Answer · 2013-07-20T17:23:53

The exception means that the source of the Linq query (groups) is null. You need to make sure that ViewBag.Groups is initialized (this does not happen anywhere in your posted code).

Did you want Model.Groups instead?

Can not understand why i am getting System.ArgumentNullException was unhandled by user code

1 Answers