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

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

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 2

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.