c# - 无法在 MVC 操作中返回 CSV 文件。 Not 无法访问已关闭的 Streamable

Question

在 ASP.NET MVC 操作中，我试图返回包含用户信息的 CSV 文件:

  IList<UserModel> users = _repository.GetUsers();

  MemoryStream stream = new MemoryStream;
    using (StreamWriter writer = new StreamWriter(stream)) {
      using (CsvWriter csv = new CsvWriter(writer)) {
        csv.Configuration.With(x => {
          x.AutoMap<UserModel>();
          x.RegisterClassMap<UserModelCsvMapper>();
        });            
        csv.WriteRecords(reply.Users);
        writer.Flush();
        return File(stream, "text/csv", "Users.csv");
      }
    }

我有以下映射器:

public class UserModelCsvMapper : CsvClassMap<UserModel> {
  public override void CreateMap() {
    Map(x => x.Name).Name("Name");
    Map(x => x.Email).Name("Email");
    Map(x => x.Linked).Name("Linked");
  } // CreateMap
} // UserModelCsvMapper

我的 CSV 编写器似乎是空的，当我返回 Stream 时出现错误:

((System.IO.Stream)(stream)).WriteTimeout' threw an exception of type 'System.InvalidOperationException'

我得到错误页面:

Cannot access a closed Stream.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ObjectDisposedException: Cannot access a closed Stream.

更新:添加堆栈跟踪

无法访问已关闭的 Stream。
说明:执行当前 Web 请求期间发生未处理的异常。请查看堆栈跟踪以获取有关错误及其源自代码的位置的更多信息。

异常详细信息:System.ObjectDisposedException:无法访问已关闭的流。

源错误:

在执行当前 Web 请求期间生成了未处理的异常。可以使用下面的异常堆栈跟踪来识别有关异常起源和位置的信息。

堆栈跟踪:

[ObjectDisposedException:无法访问已关闭的流。]
System.IO._Error.StreamIsClosed() +57
System.IO.MemoryStream.Read(Byte[] buffer, Int32 offset, Int32 count) +10909062
System.Web.Mvc.FileStreamResult.WriteFile(HttpResponseBase 响应)+157
System.Web.Mvc.FileResult.ExecuteResult(ControllerContext 上下文)+296
System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult) +39
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList 1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +116
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList 1 个过滤器，Int32 filterIndex，ResultExecutingContext preContext，ControllerContext controllerContext，ActionResult actionResult) +529
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList 1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +529
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList 1 个过滤器，ActionResult actionResult) +106
System.Web.Mvc.Async.<>c_DisplayClass2b.b_1c() +321
System.Web.Mvc.Async.<>c_DisplayClass21.b_1e(IAsyncResult asyncResult) +185
System.Web.Mvc.Async.WrappedAsyncResult 1.CallEndDelegate(IAsyncResult asyncResult) +42
System.Web.Mvc.Async.WrappedAsyncResultBase 1.结束()+133
System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, 对象标签) +56
System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +40
System.Web.Mvc.Controller.b_1d(IAsyncResult asyncResult, ExecuteCoreState innerState) +34
System.Web.Mvc.Async.WrappedAsyncVoid 1.CallEndDelegate(IAsyncResult asyncResult) +70
System.Web.Mvc.Async.WrappedAsyncResultBase 1.结束()+139
System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, 对象标签) +59
System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40
System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +44
System.Web.Mvc.Controller.b_15(IAsyncResult asyncResult， Controller Controller )+39
System.Web.Mvc.Async.WrappedAsyncVoid 1.CallEndDelegate(IAsyncResult asyncResult) +62
System.Web.Mvc.Async.WrappedAsyncResultBase 1.结束()+139
System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, 对象标签) +59
System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40
System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +39
System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.EndExecute(IAsyncResult asyncResult) +39
System.Web.Mvc.MvcHandler.b_5(IAsyncResult asyncResult, ProcessRequestState innerState) +39
System.Web.Mvc.Async.WrappedAsyncVoid 1.CallEndDelegate(IAsyncResult asyncResult) +70
System.Web.Mvc.Async.WrappedAsyncResultBase 1.结束()+139
System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, 对象标签) +59
System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40
System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +40
System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult 结果) +38
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +9514928
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

谢谢，
米格尔

Answer 1

您的 using 语句正在关闭您在 FileResult 中返回的内存流。

这应该解决它。声明 MemoryStream block 外。一旦流被完全写入 Response，它将被框架关闭。流(虽然目前没有必要关闭 MemoryStream 。当它们被垃圾收集时，它们会被正确清理。

IList<UserModel> users = _repository.GetUsers();

var stream = new MemoryStream();
using (StreamWriter writer = new StreamWriter(stream)) {
  using (CsvWriter csv = new CsvWriter(writer)) {
      csv.Configuration.With(x => {
      x.AutoMap<UserModel>();
      x.RegisterClassMap<UserModelCsvMapper>();  
    });            
    csv.WriteRecords(reply.Users)
    writer.Flush();
    return File(stream, "text/csv", "Users.csv");
  }
}

或者，您可以使用 FileResponse 的 Byte[] 重载。

using (var stream = new MemoryStream())
using (StreamWriter writer = new StreamWriter(stream))
using (CsvWriter csv = new CsvWriter(writer) {
  csv.Configuration.With(x => {
    x.AutoMap<UserModel>();
    x.RegisterClassMap<UserModelCsvMapper>();  
  })        

  //use the users that you just retrieved from the repository
  csv.WriteRecords(users)
  writer.Flush();

  return File(stream.ToArray(), "text/csv", "Users.csv");
}