MVC Pass generic list to controller action from JS file

Question

I have a text file and when users upload the file, the controller action method parses that file using state machine and uses a generic list to store some values. I pass this back to the page in the form of a hidden field. Users can then click on a link which invoked a JS modal dialoag box and they could see the list and add comments for each item in the list. When they click on the link I am trying to post to an action method which would take that hidden field and do something with it and render a partial view. The problem is when i post to this action method, this field is being passed as null.

here is my code

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



if (Model.ExceptionString != null)
           {
               if (Model.ExceptionString.Count > 0)
               {
        <div class="bodyContent">
            <span class="leftContent">
                @Html.Label("Test Exceptions")
            </span><span class="rightContent"><span id="TestExceptionChildDialogLink" class="treeViewLink">Click
                here to View Test Exceptions</span>
                <br />
                <span id="TestExceptionDisplay"></span>
                @Html.HiddenFor(model => model.ExceptionString)
                <input id="ExceptionString" type="hidden" value="@Model.ExceptionString" />
            </span>
        </div>
               }
           }

<div id="testExceptiontreeview" title="Dialog Title" style="font-size: 10px; font-weight: normal;
    overflow: scroll; width: 800px; height: 450px;">
    <div id="testExceptions">

    </div>
    <div id="inputTestExceptions" style="display: none;">
    </div>
</div>


  var runlogTestExceptionUrl = '@Url.Action("ListTestExceptions", "RunLogEntry")';

JS FILE

 $("#inputTestExceptions").load(runlogTestExceptionUrl, { ExceptionStrings: $("#ExceptionString").val() });

Controller action

[HttpPost]
        public ViewResult ListTestExceptions(List<string> ExceptionStrings)
        {

Any ideas as to why exception string list is null while being passed by the JS to the abive action method?

Slider345 · Accepted Answer · 2012-09-19 16:13:09Z

$("#ExceptionString").val() is going to return a single string. This means your call to .load is just posting a single name/value pair to your MVC application.

You need it to be posting a collection of name/value pairs. The name will be the same: the name of the collection with an indexer. The value will be the exception string. This is going to take some significant refactoring.

Here's basic way this could work:

View code:

<form action="@Url.Action("ListTestExceptions", "RunLogEntry")" TYPE="POST">
@{ int counter = 0;}
@foreach(var exception in Model.ExceptionString)
{

  <input id='@("ExceptionString["+counter+"]")' type="hidden" value='@exception' />
  @{ counter =counter + 1; }
}
</form>

JS code:

$.ajax({
        url: runlogTestExceptionUrl,
        data: $(this).serialize(),
        success: function(data) {
             $('#inputTestExceptions').html(data);
        }
});

Controller action is unchanged:

[HttpPost]
    public ViewResult ListTestExceptions(List<string> ExceptionStrings)
    {

Obviously this isn't going to integrate instantly with your code. But this would be the way to post data from a form to a single collection variable in MVC.

Note: I'm a little rusty on the razor syntax so there may be some little syntax issues. I'll fix them as I find them.

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