Hiddenfor not getting correct value from view model

I have a multi-step file import process. I have a hidden form input in my view that I am trying to populate with the "CurrentStep" from the view model.

<% = Html.HiddenFor(model => model.CurrentStep) %>

CurrentStep is an Enum and I always get the default value rather than the one I provided to the view model. on the other hand this gets me the correct value:

<p><% = Model.CurrentStep %></p>

I realise I could just hand code the hidden input but I want to know: what am I doing wrong? Is there a better way to keep track of the current step between POSTs?

Solution 1:

What you are doing wrong is that you are trying to modify the value of a POSTed variable in your controller action. So I suppose you are trying to do this:

[HttpPost]
public ActionResult Foo(SomeModel model)
{
    model.CurrentStep = Steps.SomeNewValue;
    return View(model);
}

and html helpers such as HiddenFor will always first use the POSTed value and after that the value in the model.

So you have a couple of possibilities:

1. Remove the value from the modelstate:

   [HttpPost]
   public ActionResult Foo(SomeModel model)
   {
       ModelState.Remove("CurrentStep");            
       model.CurrentStep = Steps.SomeNewValue;
       return View(model);
   }
   

2. Manually generate the hidden field

   <input type="hidden" name="NextStep" value="<%= Model.CurrentStep %>" />
   

3. Write a custom helper which will use the value of your model and not the one that's being POSTed

Solution 2:

My solution was to use Darin's second option, because option 1 (clearing from the model state) means hard coding a string (and the naming convention can be tricky with complex models), and wanted to avoid option 3 because I already have so many custom helpers.

<input type="hidden" name="@Html.NameFor(x => Model.SomeId)" value="@Model.SomeId" />

Just a reminder that you can use Html.NameFor to keep things clean.