asp.net sending a List<> of items to controller

Question

I have the following form:

 <li>
                                    <% using (Html.BeginForm("TestMethod", "MyController", FormMethod.Post, new {id = "TestMethod"}))
                                       {%>
                                           <%= Html.Hidden("model", Model.MyListOfObjects) %>

                                     <%}%>
                                      <a href="#" onclick="SubmitForm()">Test</a>
                                   </li>

And the javascript function for the onclick is as follows:

   function SubmitForm() {
  document.forms["TestMethod"].submit();
 }

I am trying to pass the list of objects from the view into the controller, but i have yet managed to get this to work. My Controller function is:

 [Authorize]
    [HttpPost]
    public ActionResult TestMethod(List<Objects> model)
    {
        dynamic Expando = new ExpandoObject();
        Expando.test = model; 
        return View(Expando );
    }

When I view the List of objects in the debugger it always displays "System.Collections.Generic.List`1[]" with no actual objects inside.

So my question is what should I be doing to pass a List of objects into a controller?

I have also tried:

 <% using (Html.BeginForm("TestMethod", "MyWork", FormMethod.Post, new {id = "TestMethod"}))
                                       {%>
                                       <% int itemx = 0; %>
                                       <% foreach (var x in Model.MyListOfObjects)
                                          {%>
                                            <%= Html.Hidden("model"+"["+itemx+"]", x) %>
                                            <%itemx++; %>
                                          <% } %>


                                     <%}%>

score 1 · Accepted Answer · edited May 23 '17 at 11:55

You cannot just put List<object> as action parameter and expect the model binder to be able to automagically guess what object types you want to put there. You will need to write a custom model binder if you wanted to handle multiple sub-types as illustrated in this post.

And if you want to use a single type for the list such as List<MyViewModel> then simply loop through each element of the list (respecting the convention) and for each element build a hidden field for each property that you want to bind.

But since those are hidden fields, I guess that the user is not supposed to modify them. In this case those hidden fields have nothing to do in your view. Let's not reinvent the ViewState that we were all so happy to get rid of when we moved to ASP.NET MVC from classic WebForms. Simply put a hidden field containing an unique id that will allow you to refetch the corresponding list elements in the POST action given this unique id from wherever you fetched them initially (your database or something I suppose).

Hi Darin, cheers for the explanation and the links. That really helped. — TBD, Mar 06 '12 at 09:02
Hello, Darin. Got a similar question around here, care to check it out? https://stackoverflow.com/questions/47279288/submit-a-form-with-multiple-objects-to-the-controller — Luis Alberto Delgado de la Flo, Nov 14 '17 at 23:01

score 0 · Answer 2 · answered Mar 05 '12 at 17:06

0

You need to have one hidden element for each object in the list, and named model[0], model[1], etc.

answered Mar 05 '12 at 17:06

GriffeyDog

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Hi, cheers for the answer. Doing this gave me a list, but all the objects in the list just contained "System.Collections.Generic.List". – TBD Mar 05 '12 at 17:32
Are the elements of Model.MyListOfObjects also Lists themselves? – GriffeyDog Mar 05 '12 at 19:10

asp.net sending a List<> of items to controller

2 Answers2