ASP.NET MVC表单的简单验证失败

<%=Html.ValidationSummary() %>
    <table>
        <tr>
            <td>
                Feed Url:
            </td>
            <td>
                <%=Html.TextBox("url", null, new {@style="width:300px"}) %>
            </td>
        </tr></table>

我的控制器也很简单:

[AcceptVerbs(HttpVerbs.Post)]
    public ActionResult AddFeed(FormCollection collection)
    {
        string url = collection.Get("url");
        string roles = collection.Get("Roles");
        if (string.IsNullOrEmpty(url))
        {
            ModelState.AddModelError("url", "Please provide a propre feed url");
        }
        if (string.IsNullOrEmpty(roles))
        {
            ModelState.AddModelError("Roles", "Please select a valid role");
        }
        if (ModelState.IsValid)
        {
            Session["url"] = url;
            Session["Roles"] = roles;
            return RedirectToAction("ValidateFeed");
        }
        else
        {
            return View();
        }
    }

/H4mm3r型

请忽略Roles元素,我有一个下拉列表,但为了简单起见从标记中删除了它