枚举反射程序集中的集合需要空引用检查吗？

Question

我在 C#/.NET 3.5 中遇到了一种非常奇怪的行为...

我正在编写一个挂钩到内容管理系统的上传管道的类。 CMS 通过反射执行该钩子。

由于某些未知原因，以下代码失败并抛出 NullRef（“Files”是一个 HttpFileCollection）。

foreach (var fileKey in args.Files.AllKeys)
{
     // Do Stuff
}

在语句之前添加 NullRef 检查后，循环将成功。两种情况下上传的文件都是相同的。 return 语句永远不会被执行，因为 null 条件失败。

if (args.Files == null ) return;
foreach (var fileKey in args.Files.AllKeys)
{
   // Do Stuff
}

我完全被这个难住了。有什么想法吗？

完整堆栈跟踪

    ** Exception: System.Web.HttpUnhandledException **
    Message: Exception of type 'System.Web.HttpUnhandledException' was thrown.
    Source: System.Web
    at System.Web.UI.Page.HandleError(Exception e)
    at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
    at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
    at System.Web.UI.Page.ProcessRequest()
    at System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context)
    at System.Web.UI.Page.ProcessRequest(HttpContext context)
    at ASP.sitecore_shell_applications_flashupload_advanced_uploadtarget_aspx.ProcessRequest(HttpContext context)
    at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
    at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

    ** Nested Exception ** 
    Exception: System.Reflection.TargetInvocationException
    Message: Exception has been thrown by the target of an invocation.
    Source: mscorlib
    at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes,        RuntimeTypeHandle typeOwner)
    at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes,        RuntimeTypeHandle typeOwner)
    at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
    at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
    at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
    at Sitecore.Reflection.ReflectionUtil.InvokeMethod(MethodInfo method, Object[] parameters, Object obj)
    at Sitecore.Pipelines.Processor.Invoke(PipelineArgs args)
    at Sitecore.Nexus.Pipelines.NexusPipelineApi.Resume(PipelineArgs args, Pipeline pipeline)
    at Sitecore.Pipelines.Pipeline.Resume()
    at Sitecore.Pipelines.Pipeline.DoStart(PipelineArgs args)
    at Sitecore.Pipelines.Pipeline.Start(PipelineArgs args, Boolean atomic)
    at Sitecore.Pipelines.Pipeline.Start(PipelineArgs args)
    at Sitecore.Shell.Applications.FlashUpload.Advanced.UploadTarget.HandleUpload()
    at Sitecore.Shell.Applications.FlashUpload.Advanced.UploadTarget.OnLoad(EventArgs e)
    at System.Web.UI.Control.LoadRecursive()
    at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

    ** Nested Exception **
    Exception: System.NullReferenceException
    Message: Object reference not set to an instance of an object.
    Source: Sitecore.CustomExtensions
    at Sitecore.CustomExtensions.StreamingMediaUploader.Process(UploadArgs args) in C:\...\Sitecore.CustomExtensions\StreamingMediaUploader.cs:line 33

Answer 1

只是猜测，但 CMS 中可能存在一些意外行为（可能是错误）。无论是否有错误，您与 CMS 的合同尚未完全定义。

上传的文件匹配的原因是因为您的方法可能被多次调用，最后一次调用引发异常。

鉴于您正在使用一个不受您控制的应用程序，您的解决方案是正确的 - 您必须在使用它之前检查所提供的所有内容。