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