回发后未出现在 MVC Model 中的隐藏表单字段

Question

I have a new MVC 4 Application with a fairly basic View/Controller. The associated Model contains a couple properties that I've mapped to Hidden form fields. When the Page renders the first time ( eg via the HttpGet Action ) it all looks fine. But when the form is Post'ed by selecting the Submit button the resulting Model presented to the Action no longer has the Hidden field values set. Here is a walkthrough of the particulars.

Here is a sample of the Model :

public class Application
{
    public bool ShowSideBars { get; set; }
}

Here is the initial Controller * Action * ( which seems to work fine ):

[HttpGet]
public ActionResult Application()
{
    var model = Request.ParseFromQueryString<Application>();
    model.ShowSideBars = true;

    return View(model);
}

This maps to the View as follows:

<fieldset>
    @Html.HiddenFor(m => m.ShowSideBars)
...
</fieldset>

This results in the following mark-up to be rendered inside the fieldset:

<input data-val="true" data-val-required="The ShowSideBars field is required." id="ShowSideBars" name="ShowSideBars" type="hidden" value="True" />

Note : I sure wish I knew why MVC has decided to add the '... field is required' content when I didn't flag it as required, but that's for another question

Here is the Action that is called when the form is submitted. At this point the aforementioned property will no longer be set to ' true '.

[HttpPost]
public ActionResult Application(Application application)
{
    // Other work done here

    return View(application);
}

At present, there are no custom Model Binders. Also, I've tested some other data types and I'm seeing the same thing.

Can someone explain why hidden form values are not being returned? Am I just doing this all wrong?

Answer 1

If you have the property in your model decorated with a ReadOnlyAttribute the value will not be populated back into the model for you. After all, it is read only.

Answer 2

I cannot reproduce the issue (ASP.NET MVC 4 Beta running on VS 2010 .NET 4.0).

Model:

public class Application
{
    public bool ShowSideBars { get; set; }
}

Controller:

public class HomeController : Controller
{
    public ActionResult Application()
    {
        var model = new Application();
        model.ShowSideBars = true;
        return View(model);
    }

    [HttpPost]
    public ActionResult Application(Application application)
    {
        return Content(application.ShowSideBars.ToString());
    }
}

View:

@model Application

@using (Html.BeginForm())
{
    @Html.HiddenFor(m => m.ShowSideBars)
    <button type="submit">OK</button>
}

When I submit the form, the model binder correctly assigns the ShowSideBars property in the POST action to true.

Note: I sure wish I knew why MVC has decided to add the '... field is required' content when I didn't flag it as required, but that's for another question

That's because non-nullable types such as booleans are always required. You could stop ASP.NET MVC helpers from emitting HTML5 data-* client side validation attributes for them by putting the following line in Application_Start :

DataAnnotationsModelValidatorProvider.AddImplicitRequiredAttributeForValueTypes = false;

Answer 3

我认为字段必须在html标签的形式内，以便隐藏的字段被回发而不被忽略

Answer 4

I just had the same problem. The form didn't submitted the hidden property because the model class didn't had a proper getter and setter for that property. I know that is not the issue you had, just figured it might help other people that will lend in this page.

Answer 5

try this:

public class Model
{
    [ScaffoldColumn(false)]
    public bool InvisibleProperty { get; set; }
}

more info here (ScaffoldColumn(bool value) vs HiddenInput(DisplayValue = bool value) in MVC)

Answer 6

In my case it was because I had declared a field instead of a property:

public BaseController.Modes Mode;

doesn't work. But:

public BaseController.Modes Mode { get; set; }

works. The default model binder only works with properties.

Answer 7

I kid you not, this is another reason it could happen.

My form had the same field in it twice. The other field was actually not in the form, but that doesn't matter.

Run this jQuery in the developer console to see how many elements come back:

$("[id$=PropertyName]"); // Search for ids ending with property name.

Example:

Answer 8

For me, in Core 6 the solution was removing [Editable(false)] attribute from the model class Id property which I wanted to tunnel through get/post as a hidden form field. In.Net 4.8 it was not a problem.