问题:

I wanna do something like this:

[HttpPost]
public ActionResult Index(Foo foo)
{
    foo.Name = "modified";

    return View(foo);
}

but when my view is rendered, it always has the old values! How can I modify and return? Must I clear the ModelState everytime?

My view:

@model MvcApplication1.Models.Foo


@using (Html.BeginForm())
{
    @Html.TextBoxFor(m => m.Name)
    @Html.TextBoxFor(m => m.Description)

    <input type="submit" value="Send" />
}

回答1:

I think this might be expected behavior because the "normal" scenario where you send back the same model to the view is when the model has errors.

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

回答2:

MVC uses ModelState on postback to populate the View, not the passed model. To update a single field before returning to the view try something like this:

var newVal = new ValueProviderResult("updated value", "updated value", CultureInfo.InvariantCulture);
ModelState.SetModelValue("MyFieldName", newVal);

More info here: ModelStateDictionary.SetModelValue()