ASP.Net MVC 2.0 Html.HiddenFor HtmlHelper extension doesn't return the Value

We're trying to be type-safe in our views and use the new ExpressionInputExtenssion HtmlHelpers, but we are seeing some inconsistent results. We have a view that looks like this:

ViewData.Model.FooID = <%= ViewData.Model.FooID %><
Model.FooID = <%= Model.FooID  %>       
<%= Html.HiddenFor(x=>x开发者_高级运维.FooID) %>  

But what we see in the rendered view is this:

ViewData.Model.FooID = 515b0403-e75b-4bd7-9b60-ef432f39d338
Model.FooID = 515b0403-e75b-4bd7-9b60-ef432f39d338    
<input id="FooID" name="FooID" type="hidden" value="" />  

I can manually add this:

<input id="FooID" name="FooID" type="hidden" value="<%= Model.FooID %>" />

But now we are no longer, but surprisingly when I do, The Html.HiddenFor always has the correct value.

Take a look at this: http://blogs.msdn.com/b/simonince/archive/2010/05/05/asp-net-mvc-s-html-helpers-render-the-wrong-value.aspx

It looks like the model binder that is behind the extension method cannot convert you FoodID datatype to a string. Is your data type a regular GUID?

I known there are overloads for this extension method for working with binary but I'm not sure about GUIDs ....

Have u tried debbuging it?

I encountered similiar problem, I have one element of the model is hiddeninput, I can see the correct value of this element while displaying view(as debug I show it to check there's correct value in the view), but once I post the view, the return value of this element keeps the first time it's been set, whatever I refresh the display and be sure the correct value shown on the view, but the return value just keep the value been set at first time. This is odd.

You can also roll your own extension that use the value from the property

@Html.HiddenForField(m => m.Location.CityRequired)

public static class HiddenExtensions
{
    public static MvcHtmlString HiddenForField<TModel, TValue>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TValue>> expression) where TModel : class
    {
        var metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
        var value = metadata.Model;
        return htmlHelper.HiddenForField(expression, value);
    }

    public static MvcHtmlString HiddenForField<TModel, TValue>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TValue>> expression, object value) where TModel : class
    {
        string htmlFieldName = ExpressionHelper.GetExpressionText(expression);
        string fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(htmlFieldName);
        var tag = new TagBuilder("input");
        tag.GenerateId(fullName);
        tag.Attributes.Add("type", "hidden");
        tag.Attributes.Add("name", fullName);
        tag.Attributes.Add("value", value != null ? value.ToString() : string.Empty);
        return new MvcHtmlString(tag.ToString());
    }
}