为什么关闭流上的ASP.NET MVC控制器FileStreamResult错误？

Question

我试图从派生自列表的MVC控制器返回csv文件。基于结合我从文档和SO问题中读取的内容，我提出了以下控制器代码。我一定想念一些东西，因为我因“无法访问封闭的流”而出现黄屏死机...

public class ConsumersFileController : Controller
{
    private readonly TDCContext _db = new TDCContext();


    public ActionResult Index()
    {
        IEnumerable<Consumer> list = _db.Consumers.ToList();

        //put List in memory stream object
        MemoryStream memoryStream = new MemoryStream();
        using (memoryStream)
        {
            //return memory stream as file stream result:
            using (BinaryWriter binaryWriter = new BinaryWriter(memoryStream, System.Text.Encoding.UTF8, true))
            {
                foreach (var item in list)
                {
                    var itemBytes = item.Serialize();
                    binaryWriter.Write(itemBytes.Length);
                    binaryWriter.Write(itemBytes);

                }

                FileStreamResult fileStream =
                    new FileStreamResult(memoryStream, "application/txt") {FileDownloadName = "zips.csv"};

                return fileStream;
            }
        }
    }

    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            _db.Dispose();
        }
        base.Dispose(disposing);
    }

}

这是堆栈跟踪：

[ObjectDisposedException: Cannot access a closed Stream.]
   System.IO.__Error.StreamIsClosed() +59
   System.IO.MemoryStream.Read(Byte[] buffer, Int32 offset, Int32 count) +14731549
   System.Web.Mvc.FileStreamResult.WriteFile(HttpResponseBase response) +93
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +88
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +831
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +81
   System.Web.Mvc.Async.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult) +185
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +38
   System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(IAsyncResult asyncResult, ExecuteCoreState innerState) +29
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +67
   System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +52
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +36
   System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +38
   System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__5(IAsyncResult asyncResult, ProcessRequestState innerState) +43
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +67
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +38
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +607
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +134

如果要using在流的块内返回结果，如何关闭流？

Answer 1

您应该删除：

using (memoryStream)

FileStreamResult会为你处理memoryStream。

您的代码不起作用的原因是，从中读取的实际工作memoryStream不在您的代码中，而是在调用的MVC代码中fileStream.WriteFile。但是该代码在调用堆栈的更高位置执行。到了WriteFile被称为（需要memoryStream）的时间，您已经将其处置了。