MVC3 asp.net error: Value cannot be null. Parameter name: items on dropdownlist

Question

I am getting a dump ONLY in the server and not in my local system when trying to post the data. There is a page which submits some value to the database. I have also modeled the dropdown in the page as mandatory. However, when clicking on "Create", instead of giving an error like "Missing"; it throws a dump.

Dump trace:

Value cannot be null.
Parameter name: items

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.ArgumentNullException: Value cannot be null.
Parameter name: items

Source Error: 


Line 65:         </div>
Line 66:         <div class="editor-field">
Line 67:             @Html.DropDownListFor(x => x.ProjectName, new SelectList(Model.ProjectDetail, "ProjectName", "ProjectName"),"")
Line 68:             <span runat="server" style="color:Red;" visible="false"> *</span>
Line 69:             @Html.ValidationMessageFor(model => model.ProjectName)

Source File: d:\hosting\11178048\html\fbpm\fbpm\Views\User\Create.cshtml    Line: 67 

Stack Trace:

[ArgumentNullException: Value cannot be null. Parameter name: items]   System.Web.Mvc.MultiSelectList..ctor(IEnumerable items, String dataValueField, String dataTextField, IEnumerable selectedValues)
+289714    System.Web.Mvc.SelectList..ctor(IEnumerable items, String dataValueField, String dataTextField) +19    ASP._Page_Views_User_Create_cshtml.Execute() in d:\hosting\11178048\html\fbpm\fbpm\Views\User\Create.cshtml:67    System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +197    System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +81    System.Web.WebPages.StartPage.RunPage() +17

The Controller code:

public ActionResult Create()
{
    var model = new UserDetail
    {
        ProjectDetail = db1.ProjectDetails.ToList()
    };
    return View(model);
} 

//
// POST: /User/Create

[HttpPost]
public ActionResult Create(UserDetail userdetail)
{
    if (ModelState.IsValid)
    {
        db.UserDetails.Add(userdetail);
        db.SaveChanges();
        return RedirectToAction("SearchCust");  
    }

    return View(userdetail);
}

The view code:

@model fbpm.Models.UserDetail

@{
    ViewBag.Title = "Create Customer";
}

<h2>Create Customer</h2>

<script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>

@using (Html.BeginForm()) {
    @Html.ValidationSummary(true)
    <fieldset>
        <legend>Customer Detail</legend>
        <div id ="left" style="float:left; width:400px;">
        <div class="editor-label">
            @Html.LabelFor(model => model.UserID)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.UserID)
            <span runat="server" style="color:Red;" visible="false"> *</span>
            @Html.ValidationMessageFor(model => model.UserID)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Password)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Password)
            <span runat="server" style="color:Red;" visible="false"> *</span>
            @Html.ValidationMessageFor(model => model.Password)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.UserName)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.UserName)
            @Html.ValidationMessageFor(model => model.UserName)
        </div>
        <div class="editor-label">
            @Html.LabelFor(model => model.PANNo)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.PANNo)
            @Html.ValidationMessageFor(model => model.PANNo)
        </div>
        <div class="editor-label">
            @Html.LabelFor(model => model.EmailID)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.EmailID)
            @Html.ValidationMessageFor(model => model.EmailID)
        </div>
        <br />
        <p>
            <input type="submit" value="Create Customer" />
        </p>

        </div>
        <div id = "left3" style="float:left; width:400px">
        <div class="editor-label">
            @Html.LabelFor(model => model.ProjectName)
        </div>
        <div class="editor-field">
            @Html.DropDownListFor(x => x.ProjectName, new SelectList(Model.ProjectDetail, "ProjectName", "ProjectName"),"")
            <span runat="server" style="color:Red;" visible="false"> *</span>
            @Html.ValidationMessageFor(model => model.ProjectName)
        </div>
        <div class="editor-label">
            @Html.LabelFor(model => model.BookedDate)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.BookedDate)
            <span runat="server" style="color:Red;" visible="false"> *</span>
            @Html.ValidationMessageFor(model => model.BookedDate)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.BookedAmount)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.BookedAmount)
            <span runat="server" style="color:Red;" visible="false"> *</span>
            @Html.ValidationMessageFor(model => model.BookedAmount)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Contact1)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Contact1)
            @Html.ValidationMessageFor(model => model.Contact1)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Contact2)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Contact2)
            @Html.ValidationMessageFor(model => model.Contact2)
        </div>
        </div>
        <div id="left1" style="float:left; width:400px;">
        <div class="editor-field">
            @Html.HiddenFor(model => model.Role, new { @readonly = "readonly", @Value = "400" })
            @Html.ValidationMessageFor(model => model.Role)
        </div>
        <div class="editor-label">
            @Html.LabelFor(model => model.FullAddress)
        </div>
        <div class="editor-field">
            @Html.TextAreaFor(model => model.FullAddress)
            @Html.ValidationMessageFor(model => model.FullAddress)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.State)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.State)
            @Html.ValidationMessageFor(model => model.State)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Country)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Country)
            @Html.ValidationMessageFor(model => model.Country)
        </div>


        </div>

    </fieldset>
}

<div>
    @Html.ActionLink("Back to List", "SearchCust")
</div>

I have searched a lot in the net and found that adding a viewbag for the project name in the submit action before returning the view owuld help; but, it didnt. Please can someone help?

Regards

Answer 1

I'm assuming you only see this exception when your insert fails; you then try to reuse the UserDetail model in the view for the same page.

The error you are seeing is due to the nature of working with HTTP - anything that is not directly bound to an input is not retained. So, when you attempt to rebuild the view, the list you are trying to bind the drop-down helper to is null, since UserDetail.ProjectDetail has not been repopulated. You can fix this like so:

[HttpPost]
public ActionResult Create(UserDetail userdetail)
{
    if (ModelState.IsValid)
    {
        db.UserDetails.Add(userdetail);
        db.SaveChanges();
        return RedirectToAction("SearchCust");  
    }

    userdetail.ProjectDetail = db1.ProjectDetails.ToList();

    return View(userdetail);
}

Answer 2

I noticed that create button is a submit button

So it must call action with HttpPost attribute [HttpPost] public ActionResult Create(UserDetail userdetail)

In this action, it returns View(userdetail);

But this userdetail object is created by model binder from the submit data from browser. So it won't have values in ProjectDetail property.

You can step it through