没有Request,也没有使用FormCollection。
       [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult Create(int CategoryID, FormCollection form)
        {
            var model = db.Categories.FirstOrDefault(c=>c.CategoryID==CategoryID);
            if (model == null)
            {
                Categories category = new Categories();
                UpdateModel(category, new[] { "CategoryName", "Description" });
                db.AddToCategories(category);
                db.SaveChanges();
                return RedirectToAction("Index");
            }
            return RedirectToAction("Create");
        }<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<MyMVCDemo.Categories>" %><asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
Create
</asp:Content><asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">    <h2>Create</h2>    <% using (Html.BeginForm()) {%>
        <%= Html.ValidationSummary(true) %>        <fieldset>
            <legend>Fields</legend>
            
            <div class="editor-label">
                <%= Html.LabelFor(model => model.CategoryID) %>
            </div>
            <div class="editor-field">
                <%= Html.TextBoxFor(model => model.CategoryID) %>
                <%= Html.ValidationMessageFor(model => model.CategoryID) %>
            </div>
            
            <div class="editor-label">
                <%= Html.LabelFor(model => model.CategoryName) %>
            </div>
            <div class="editor-field">
                <%= Html.TextBoxFor(model => model.CategoryName) %>
                <%= Html.ValidationMessageFor(model => model.CategoryName) %>
            </div>
            
            <div class="editor-label">
                <%= Html.LabelFor(model => model.Description) %>
            </div>
            <div class="editor-field">
                <%= Html.TextBoxFor(model => model.Description) %>
                <%= Html.ValidationMessageFor(model => model.Description) %>
            </div>
            
            <p>
                <input type="submit" value="Create" />
            </p>
        </fieldset>    <% } %>    <div>
        <%= Html.ActionLink("Back to List", "Index") %>
    </div></asp:Content>