C# 当控制器返回图像文件（非视图结果类型）时，为什么MVC中涉及_ViewStart？

使用ASP.NET 4.6 MVC 5，我有一个控制器操作返回gif图像（因此，不是视图），如下所示：

[Route("Content/Images/GetThatGifImage.gif", Name = "Get the gif image")]

public ActionResult GetThatGif()
{
    // Some logic here...

    return new FilePathResult("TheGifImage.gif", "image/gif")); 
}

@{
    Layout = "~/Views/Shared/TheLayout.cshtml";
}

at ASP._Page_Views_Shared_TheLayout_cshtml.Execute() in c:\inetpub\ewp\Views\Shared\TheLayout.cshtml:line 81
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.WebPages.WebPageBase.<>c__DisplayClass3.<RenderPageCore>b__2(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 StackExchange.Profiling.Mvc.WrappedView.Render(ViewContext viewContext, TextWriter writer)
at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult)
at System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(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.<BeginProcessRequest>b__5(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.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

同时，我有一个

\u ViewStart.cshtml

只做一件事：为应用程序中的所有视图定义布局。看起来像这样：

[Route("Content/Images/GetThatGifImage.gif", Name = "Get the gif image")]

public ActionResult GetThatGif()
{
    // Some logic here...

    return new FilePathResult("TheGifImage.gif", "image/gif")); 
}

@{
    Layout = "~/Views/Shared/TheLayout.cshtml";
}

at ASP._Page_Views_Shared_TheLayout_cshtml.Execute() in c:\inetpub\ewp\Views\Shared\TheLayout.cshtml:line 81
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.WebPages.WebPageBase.<>c__DisplayClass3.<RenderPageCore>b__2(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 StackExchange.Profiling.Mvc.WrappedView.Render(ViewContext viewContext, TextWriter writer)
at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult)
at System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(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.<BeginProcessRequest>b__5(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.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

TheLayout.cshtml

包含需要设置某个

ViewBag

属性的代码，否则它会正确抛出

NullReferenceException

据我所知，如果控制器返回的类型不是

ViewResult

，则不应以任何方式涉及

\u ViewStart.cshtml

。对吧?

但是，当访问者请求

Content/Images/gethatgigimage.gif

时，他们常常会被异常捕获，并得到

500内部服务器错误

。有趣的是，无论我怎么努力，我自己都无法重现这个错误。我可以在IIS服务器上的事件日志中看到访问者遇到的错误。这似乎是武断的，不是每一个请求都会发生。事件日志中的堆栈跟踪如下所示：

[Route("Content/Images/GetThatGifImage.gif", Name = "Get the gif image")]

public ActionResult GetThatGif()
{
    // Some logic here...

    return new FilePathResult("TheGifImage.gif", "image/gif")); 
}

@{
    Layout = "~/Views/Shared/TheLayout.cshtml";
}

at ASP._Page_Views_Shared_TheLayout_cshtml.Execute() in c:\inetpub\ewp\Views\Shared\TheLayout.cshtml:line 81
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.WebPages.WebPageBase.<>c__DisplayClass3.<RenderPageCore>b__2(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 StackExchange.Profiling.Mvc.WrappedView.Render(ViewContext viewContext, TextWriter writer)
at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult)
at System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(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.<BeginProcessRequest>b__5(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.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

---

最后，我的问题总结如下：

为什么?

如何解决该问题（使控制器不执行

\u ViewStart

文件）

奖金：为什么它是任意的

奖金：为什么我不能复制它？除了武断之外还有其他原因吗

---

谢谢你的帮助

我发现了这个bug，是的，它是我的：/

该操作有一个自定义操作筛选器（

OnActionExecuting

），用于从cookie中读取值。这很尴尬，但在获取值之前，我没有检查cookie是否为null（cookie缺失）。因此，当cookie丢失时，它抛出一个

NullReferenceException

。（我无法再现错误，因为在我的环境中设置了cookie。）

---

我仍然不明白为什么layout.cshtml（通过

\u ViewStart.cshtml

）会牵涉进来，给我一些误导性的错误信息。可能是因为第一个未处理的异常（我的bug）以某种方式将结果类型切换为

ViewResult

。毕竟这个动作即将显示一种“视图”，即ASP.NET死亡黄屏（YSOD）。也许它与线程有关，就像@Robert McKee建议的那样。似乎只有在

customErrors mode=“RemoteOnly”

时才会发生这种情况。如果我切换到

customErrors mode=“Off”

我会得到正确的错误信息。（我没有进一步探讨这最后一点，所以我不确定。）

只是一个粗略的猜测，但是您有一个异步调用，它抛出了一个错误，没有被捕获，并且带来的不仅仅是它本身。关闭托管在同一线程上的其他无关调用。