1

出于某种原因，我的 ASP.NET MVC3 网页不断向我抛出 NullReferenceExceptions。奇怪的是，我无法确定问题的根源。无论我在我的视图中写什么，据说第一段代码（在本例中是我的 foreach）都会导致此错误。

我的观点是这样的：

<%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<SkyLearn.Models.StartpageDataViewModel>" %>

<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
    Skylearn - Startside
</asp:Content>

<asp:Content ID="Content3" ContentPlaceHolderID="SideContent" runat="server">
        <%foreach (var category in Model.CurrentUsersCategories)
          {%>
             <div class="homecategory"><div class="homecategoryicon"></div><%: Html.DisplayFor(Title => category.Title)%></div>
        <%}%>       
</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <%: ViewBag.Message %>
</asp:Content>

这是视图模型：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Globalization;
using System.Web.Mvc;
using System.Web.Security;
using SkyLearn.Areas.Categories.Models;
using SkyLearn.Areas.Categories.Controllers;

namespace SkyLearn.Models
{
    public class StartpageDataViewModel
    {
        public List<Category> CurrentUsersCategories { get; set; }

        public StartpageDataViewModel()
        { 
           CurrentUsersCategories = new List<Category>();
        }
    }
}

最后是我从 2 个不同的控制器中使用的方法：

这是将数据放入 viewmodel 对象的那个：

public ActionResult Index()
        {
            if (Request.IsAuthenticated)
            {
                StartpageDataViewModel model = new StartpageDataViewModel();

                MembershipUser currentuser = Membership.GetUser();
                List<Category> categories = new List<Category>();

                categories = accountcontroller.getCategoriesByRoles((Guid)currentuser.ProviderUserKey);

                foreach (Category category in categories)
                {
                    model.CurrentUsersCategories.Add(category);
                } 

                ViewBag.Message = "Velkommen til Skylearn Video Tutorials " + currentuser.UserName + "!";

                return View(model);
            }
            else 
            {
                ViewBag.Message = "Log venligst ind for at benytte Skylearn Video Tutorials";

                return View();
            }
        }

这是获取一些数据的那个：

public List<Category> getCategoriesByRoles(Guid userid)
        {
            List<Category> categoriesbyrole = new List<Category>();

            MembershipUser user = Membership.GetUser(userid);

            string[] roles = Roles.GetRolesForUser(user.UserName);

            List<Category> categories = categorycontroller.getCategories();

            foreach (string role in roles)
            {
                foreach (Category category in categories)
                {
                    if (role == category.Title)
                    {
                        categoriesbyrole.Add(category);
                    }
                }
            }

            return categoriesbyrole;
        }

在我看来，无论我做什么，我都会在 foreach 上得到当前错误：

System.NullReferenceException 未被用户代码处理
Message=Object 引用未设置为对象的实例。
Source=App_Web_nvi5brwn StackTrace: at ASP.views_home_index_aspx.__RenderContent3(HtmlTextWriter __w, Control parameterContainer) in c:\Users\AronChan\Desktop\Dropbox\SkyLearn\Skylearn Website (Aron sikkerhedskopi)\SkyLearn\Views\Home\Index.aspx:line 8 在 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) 在 System.Web.UI.Control.Render(HtmlTextWriter writer) 在 System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) 在 System.Web .UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) at System.Web.UI.Control.RenderControl(HtmlTextWriter writer) at ASP.views_shared_site_master._使成为_control1(HtmlTextWriter __w, Control parameterContainer) 在 c:\Users\AronChan\Desktop\Dropbox\SkyLearn\Skylearn 网站 (Aron sikkerhedskopi)\SkyLearn\Views\Shared\Site.Master：System.Web.UI.Control 的第 34 行。 RenderChildrenInternal(HtmlTextWriter writer, ICollection children) at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) at System.Web.UI.Control.Render(HtmlTextWriter writer) at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter 适配器）在 System.Web.UI.Control.RenderControl（HtmlTextWriter writer，ControlAdapter 适配器）在 System.Web.UI.Control.RenderControl（HtmlTextWriter writer）在 System.Web.UI.Control.RenderChildrenInternal（HtmlTextWriter writer，ICollection children ) 在 System.Web.UI.Control。RenderChildren(HtmlTextWriter writer) at System.Web.Mvc.ViewPage.Render(HtmlTextWriter writer) at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter 适配器）在 System.Web.UI.Control.RenderControl（HtmlTextWriter writer）在 System.Web.UI.Page.ProcessRequestMain（布尔 includeStagesBeforeAsyncPoint，布尔 includeStagesAfterAsyncPoint）System.Web.UI.Page.ProcessRequestMain 的 RenderControl（HtmlTextWriter writer）（布尔 includeStagesBeforeAsyncPoint，布尔 includeStagesAfterAsyncPoint）System.Web.UI.Page.ProcessRequestMain 的 RenderControl（HtmlTextWriter writer）（布尔 includeStagesBeforeAsyncPoint，布尔 includeStagesAfterAsyncPoint）
内部异常：

我已经尝试了我能想到的一切。请帮帮我xD

4

1 回答 1

2

您的问题可能来自您在 Index 中的 else。在这种情况下，您没有传递模型。因此，Model在这种情况下将为空。我会尝试发送一个空的新模型进行测试和验证。

else 
        {
            ViewBag.Message = "Log venligst ind for at benytte Skylearn Video Tutorials";

            return View();
        }
于 2012-04-19T21:18:09.713 回答