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.

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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

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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?

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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.

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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());
    }
}