@Html.HiddenFor does not work on Lists in ASP.NET

Question

I'm using a model that contains a List as a property. I'm populating this list with items i grab from SQL Server. I want the List to be hidden in the view and passed to the POST action. Later on i may want to add more items to this List with jQuery which makes an array unsuitable for expansion later on. Normally you would use

@Html.HiddenFor(model => model.MyList)

to accomplish this functionality, but for some reason the List in POST is always null.

Very simple question, anyone know why MVC behaves like this?

Answer 1

Faced the same issue. Without for loop, it only posted the first element of the list. After iterating through for loop, it can keep full list and post successfully.

 @if (Model.MyList!= null)
    {
    for (int i = 0; i < Model.MyList.Count; i++)
      {
        @Html.HiddenFor(x => x.MyList[i])
      }
    }

Answer 2

I've just come across this issue and solved it simply by doing the following:

@for(int i = 0; i < Model.ToGroups.Count; i++)
{
    @Html.HiddenFor(model => Model.ToGroups[i])
}

By using a for instead of a foreach the model binding will work correctly and pick up all of your hidden values in the list. Seems like the simplest way to solve this problem.

Answer 3

It's a bit of a hack, but if @Html.EditorFor or @Html.DisplayFor work for your list, if you want to make sure it's sent on the post request but not visible, you could just style it to using display: none; to hide it instead, e.g:

<div style="display: none;">@Html.EditorFor(model => model.MyList)</div>

Answer 4

HiddenFor is not like a DisplayFor or EditorFor. It won't work with collections, only single values.

You can use the Serialize HTML helper available in the MVC Futures project to serialize an object to a Hidden field, or you will have to write the code yourself. A better solution is to simply serialize an ID of some sort and re-get the data from the database on postback.

Answer 5

What about using Newtonsoft to deserialize the object into a json string and then insert that into your Hidden field e.g. (Model.DataResponse.Entity.Commission is a List of simple "CommissionRange" objects as you'll see in the JSON)

@using (Ajax.BeginForm("Settings", "AffiliateProgram", Model.DataResponse, new AjaxOptions { UpdateTargetId = "result" }))
   {
      string commissionJson = JsonConvert.SerializeObject(Model.DataResponse.Entity.Commission);
      @Html.HiddenFor(data => data.DataResponse.Entity.Guid)
      @Html.Hidden("DataResponse_Entity_Commission", commissionJson)
      [Rest of my form]
   }

Renders as:

<input id="DataResponse_Entity_Commission" name="DataResponse_Entity_Commission" type="hidden" value="[{"RangeStart":0,"RangeEnd":0,"CommissionPercent":2.00000},{"RangeStart":1,"RangeEnd":2,"CommissionPercent":3.00000},{"RangeStart":2,"RangeEnd":0,"CommissionPercent":2.00000},{"RangeStart":3,"RangeEnd":2,"CommissionPercent":1.00000},{"RangeStart":15,"RangeEnd":10,"CommissionPercent":5.00000}]">

In my case I do some JS stuff to edit the json in the hidden field before posting back

In my controller I then use Newtonsoft again to deserialize:

string jsonCommissionRange = Request.Form["DataResponse_Entity_Commission"];
List<CommissionRange> commissionRange = JsonConvert.DeserializeObject<List<CommissionRange>>(jsonCommissionRange);

Answer 6

I've just found out (after a couple of hours of trying to figure out why model values weren't going back to the controller) that hidden for should follow the EditorFor.

Unless I am doing something else wrong this is what I found. I will not make the mistake again.

In the context of a Model that contains a list of another class.

This will NOT work:

        @{
            for (int i = 0; i < Model.Categories.Count; i++)
            {
                <tr>
                    <td>
                        @Html.HiddenFor(modelItem => Model.Categories[i].Id)
                        @Html.HiddenFor(modelItem => Model.Categories[i].ProductCategoryId)
                        @Html.HiddenFor(modelItem => Model.Categories[i].CategoryName)                            
                        @Html.DisplayFor(modelItem => Model.Categories[i].CategoryName)                            
                    </td>
                    <td>
                        @Html.HiddenFor(modelItem => Model.Categories[i].DailyPurchaseLimit)                                                        
                        @Html.EditorFor(modelItem => Model.Categories[i].DailyPurchaseLimit)
                        @Html.ValidationMessageFor(modelItem => Model.Categories[i].DailyPurchaseLimit)
                    </td>
                    <td style="text-align: center">
                        @Html.HiddenFor(modelItem => Model.Categories[i].IsSelected)                            
                        @Html.EditorFor(modelItem => Model.Categories[i].IsSelected)
                    </td>
                </tr>
            }
        }

Where as this WILL......

            for (int i = 0; i < Model.Categories.Count; i++)
            {
                <tr>
                    <td>
                        @Html.HiddenFor(modelItem => Model.Categories[i].Id)
                        @Html.HiddenFor(modelItem => Model.Categories[i].ProductCategoryId)
                        @Html.HiddenFor(modelItem => Model.Categories[i].CategoryName)                            
                        @Html.DisplayFor(modelItem => Model.Categories[i].CategoryName)                            
                    </td>
                    <td>
                        @Html.EditorFor(modelItem => Model.Categories[i].DailyPurchaseLimit)
                        @Html.HiddenFor(modelItem => Model.Categories[i].DailyPurchaseLimit)                            
                        @Html.ValidationMessageFor(modelItem => Model.Categories[i].DailyPurchaseLimit)
                    </td>
                    <td style="text-align: center">
                        @Html.EditorFor(modelItem => Model.Categories[i].IsSelected)
                        @Html.HiddenFor(modelItem => Model.Categories[i].IsSelected)                            
                    </td>
                </tr>
            }