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ASP.Net MVC Html.HiddenFor with wrong value

I'm using MVC 3 in my project, and I'm seeing a very strange behavior.

I'm trying to create a hidden field for a particular value on my Model, the problem is that for some reason the value set on the field does not correspond to the value in the Model.

e.g.

I have this code, just as a test:

<%:Html.Hidden("Step2", Model.Step) %>
<%:Html.HiddenFor(m => m.Step) %>

I would think that both hidden fields would have the same value. What I do is, set the value to 1 the first time I display the View, and then after the submission I increase the value of the Model field by 1.

So, the first time I render the page both controls have the value 1, but the second time the values rendered are these:

<input id="Step2" name="Step2" type="hidden" value="2" />
<input id="Step" name="Step" type="hidden" value="1" />

As you can see, the first value is correct, but the second value seems to be the same as the first time I display the View.

What am I missing? Are the *For Html helpers caching the values in some way? If so, how can I disable this caching?.

Thanks for your help.

I just tested something else. If I remove the HiddenFor call and let only the Hidden call, but using the "Step" name, it also renders only the first value (1).
happens in get as well

D
Darin Dimitrov

That's normal and it is how HTML helpers work. They first use the value of the POST request and after that the value in the model. This means that even if you modify the value of the model in your controller action if there is the same variable in the POST request your modification will be ignored and the POSTed value will be used.

One possible workaround is to remove this value from the model state in the controller action which is trying to modify the value:

// remove the Step variable from the model state 
// if you want the changes in the model to be
// taken into account
ModelState.Remove("Step");
model.Step = 2;

Another possibility is to write a custom HTML helper which will always use the value of the model and ignore POST values.

And yet another possibility:

<input type="hidden" name="Step" value="<%: Model.Step %>" />

I really appreciated Simon Ince's blog post about this. The conclusion I take from it is to ensure your workflow is correct. So if you have accepted a valid view model and done something with it then redirect to a confirmation action, even if this also simply retreives and displays an equivalent model. This means you have a fresh ModelState. blogs.msdn.com/b/simonince/archive/2010/05/05/… (linked from a post I wrote on this today: oceanbites.blogspot.com/2011/02/mvc-renders-wrong-value.html )
I really like MVC3, but this bit is really clunky. I hope they fix it in MVC4.
Wow, this one had me going for quite a while. I basically used the first suggestion but just called ModelState.Clear() before returning. This seems to work great, is there any reason not to use Clear?
The ".Remove" didn't work for me. But ModelState.Clear() did right before the return in Controller. Custom-writing your Hidden would also work well. This all happens because developers don't want to lose their "form values" if they press "submit" and the DB doesn't save correctly. Best solution: don't name different fields on same page the same name/id.
FYI this annoying behavior was graciously carried over to ASP.NET Core in case anyone was worried things would get better
P
Peter B

I encountered the same problem when writing a Wizard that shows different parts of a larger model at every step. Data and/or Errors from "Step 1" would become mixed up with "Step 2", etc, until I finally realized that ModelState was to 'blame'.

This was my simple solution:

if (oldPageIndex != newPageIndex)
{
    ModelState.Clear(); // <-- solution
}

return View(model[newPageIndex]);

ModelState.Clear() solved my issue with sequential POST requests in a similar situation.
Thanks for the ModelState.Clear() tip Evan. This was an anomaly I have never encountered before. I had several sequential ajax.beginform posts and one of them was retaining values from a previous post. Debugging black hole. Anyone know why this gets cached?
R
Ruslan Georgievskiy

This code will not work

// remove the Step variable from the model state
// if you want the changes in the model to be
// taken into account
ModelState.Remove("Step");
model.Step = 2;

...because HiddenFor always (!) reads from ModelState not the model itself. And if it doesn't find the "Step" key it will produce the default for that variable type which will be 0 in this case

Here is the solution. I wrote it for myself but don't mind sharing it cause I see many people are struggling with this naughty HiddenFor helper.

public static class CustomExtensions
{
    public static MvcHtmlString HiddenFor2<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
    {
        ReplacePropertyState(htmlHelper, expression);
        return htmlHelper.HiddenFor(expression);
    }

    public static MvcHtmlString HiddenFor2<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, object htmlAttributes)
    {
        ReplacePropertyState(htmlHelper, expression);
        return htmlHelper.HiddenFor(expression, htmlAttributes);
    }

    public static MvcHtmlString HiddenFor2<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IDictionary<string, object> htmlAttributes)
    {
        ReplacePropertyState(htmlHelper, expression);
        return htmlHelper.HiddenFor(expression, htmlAttributes);
    }

    private static void ReplacePropertyState<TModel, TProperty>(HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
    {
        string text = ExpressionHelper.GetExpressionText(expression);
        string fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(text);
        ModelStateDictionary modelState = htmlHelper.ViewContext.ViewData.ModelState;
        ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);

        if (modelState.ContainsKey(fullName))
        {                
            ValueProviderResult currentValue = modelState[fullName].Value;
            modelState[fullName].Value = new ValueProviderResult(metadata.Model, Convert.ToString(metadata.Model), currentValue.Culture);
        }
        else
        {
            modelState[fullName] = new ModelState
            {
                Value = new ValueProviderResult(metadata.Model, Convert.ToString(metadata.Model), CultureInfo.CurrentUICulture)
            };
        }
    }
}

Then you just use it as usual from within you view:

@Html.HiddenFor2(m => m.Id)

It worth to mention it works with collections too.


this solution not fully worked. After next post back property is null in Action
Well, this is the code from production where it works fine. I cannot tell why it doesn't work for you but if you see the hidden field with correct value rendered on the page I see no obvious reason why it wouldn't be restored into the model's property. If you see wrong hidden field value on the page though - that's another story, I would be very keen to know under what circumstances this happens before the same happens on my production :-) Thank you.
a
abdulkadir pekeroglu

I am too struggling with the same situation I think, where I use the same model state between calls, and when I alter a model property on backend. Though, it does not matter for me, if I use textboxfor or hiddenfor.

I just bypass the situation by using page scripts to store the model value as a js variable, because I need the hiddenfield for that purpose in the beginning.

Not sure if this helps but just consider..