问题描述
我收到一个 ArgumentNullException 异常,我不知道如何解决这个问题。 我试过 DefaultIfEmpty 但还是不行。
代码如下:
if (controller != "Home")
{
var defaultActionForController = ((List<DefaultActionForControllers>)ViewBag.DefaultActionsForControllers).Where(s => s.Controller == controller).Select(s => s.Action).FirstOrDefault();
if (controller == "ManagementObjects")
{
var controllerName = firstLayerNameSet;
@:> @Html.ActionLink(firstLayerNameSet,defaultActionForController,controller)
}
else if (controller == "MangementCategories")
{
var controllerName = secondLayerNameSet;
@:> @Html.ActionLink(secondLayerNameSet,controller)
}
else if (controller == "View")
{
@:> @Html.ActionLink(Resources.ResourceManager.GetString(controller),"","")
}
else
{
@:> @Html.ActionLink(Resources.ResourceManager.GetString(controller),controller)
}
}
这里是错误:
3005 An unhandled exception has occurred.
ArgumentNullException
Value cannot be null.
Parameter name: source
at System.Linq.Enumerable.Where[TSource](IEnumerable`1 source,Func`2 predicate)
at ASP._Page_Views_Shared__LoginPartial_cshtml.Execute() in d:\inetpub\wwwroot\TestMap\Views\Shared\_LoginPartial.cshtml:line 30
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext,TextWriter writer,WebPageRenderingBase startPage)
at System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper,String partialViewName,Object model,ViewDataDictionary viewData)
at ASP._Page_Views_Shared__TopNavbar_cshtml.Execute() in d:\inetpub\wwwroot\TestMap\Views\Shared\_TopNavbar.cshtml:line 13
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext,ViewDataDictionary viewData)
at ASP._Page_Views_Shared__Layout_cshtml.Execute() in d:\inetpub\wwwroot\TestMap\Views\Shared\_Layout.cshtml:line 73
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext,WebPageRenderingBase startPage)
at System.Web.WebPages.WebPageBase.<>c__displayClass40_0.<RenderPageCore>b__0(TextWriter writer)
at System.Web.WebPages.WebPageBase.Write(HelperResult result)
at System.Web.WebPages.WebPageBase.RenderSurrounding(String partialViewName,Action`1 body)
at System.Web.WebPages.WebPageBase.PopContext()
at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__displayClass3_1.<BeginInvokeAction>b__5(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult)
at System.Web.Mvc.Controller.<>c.<BeginExecuteCore>b__152_1(IAsyncResult asyncResult,ExecuteCoreState innerState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult)
at System.Web.Mvc.MvcHandler.<>c.<BeginProcessRequest>b__20_1(IAsyncResult asyncResult,ProcessRequestState innerState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult)
at System.Web.HttpApplication.CallHandlerExecutionStep.InvokeEndHandler(IAsyncResult ar)
at System.Web.HttpApplication.CallHandlerExecutionStep.OnAsyncHandlerCompletion(IAsyncResult ar)
这是我的 DefauftActionForControllers 的代码:
using System.Collections.Generic;
namespace Heijligers.Mas.Web.Models
{
public class DefaultActionForControllers
{
public string Controller { get; set; }
public string Action { get; set; }
}
}
我把代码改成了这个,但没有用:
var defaultActionForController = ((List<DefaultActionForControllers>)ViewContext.Controller.ViewBag.DefaultActionForControllers).FirstOrDefault(s => s.Controller == controller).Action;
它仍然给了我一个 ArgumentNullException。 当我去调试时,它说 var defaultActionForController = null 在 ViewBag.DefaultActionsForControllers 中计数 12
知道这些信息是否有任何帮助,但我想只是发布它,你永远不知道
解决方法
错误堆栈显示了问题所在:
ArgumentNullException
Value cannot be null.
Parameter name: source
at System.Linq.Enumerable.Where[TSource](IEnumerable`1 source,Func`2 predicate)
at ASP._Page_Views_Shared__LoginPartial_cshtml.Execute() in
d:\inetpub\wwwroot\TestMap\Views\Shared\_LoginPartial.cshtml:line 30
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
Where
是一个扩展方法。因此,它对源进行操作,错误告诉您 source
参数为 null
。
检查填充 ViewBag.DefaultActionsForControllers
的代码。您需要在渲染视图之前设置控制器操作的值。
最后,您的方法调用可以简化为 FirstOrDefault
也允许谓词:
var defaultActionForController = ((List<DefaultActionForControllers>)ViewBag.DefaultActionsForControllers).FirstOrDefault(s => s.Controller == controller).Action;