为什么我在这里收到"无法访问封闭的流"？

Question

堆栈跟踪看起来像

[ObjectDisposedException:无法访问已关闭的Stream.]
System.IO .__ Error.StreamIsClosed()+53
System.IO.MemoryStream.Read(Byte [] buffer,Int32 offset,Int32 count)+11411219 System.Web.Mvc.FileStreamResult. WriteFile(HttpResponseBase response)+81 System.Web.Mvc.FileResult.ExecuteResult(ControllerContext context)+168
System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext,ActionResult actionResult)+13

在调用之后

        //Byte[] bytes;
        using ( var ms = new MemoryStream() )
        {
            using ( var doc = new Document() )
            {
                using ( var writer = PdfWriter.GetInstance(doc, ms) )
                {

                    doc.Open();
                    //var example_html = @"<p>This <em>is </em><span class=""headline"" style=""text-decoration: underline;"">some</span> <strong>sample <em> text</em></strong><span style=""color: red;"">!!!</span></p>";
                    var example_html = System.IO.File.ReadAllText(Path.Combine(Server.MapPath("~/EmailTemplates"), "template.html"));
                    var example_css = @".headline{font-size:200%}";
                    using ( var srHtml = new StringReader(example_html) )
                    {
                        iTextSharp.tool.xml.XMLWorkerHelper.GetInstance().ParseXHtml(writer, doc, srHtml);
                    }
                    using ( var msCss = new MemoryStream(System.Text.Encoding.UTF8.GetBytes(example_css)) )
                    {
                        using (var msHtml = new MemoryStream(System.Text.Encoding.UTF8.GetBytes(example_html)))
                        {
                            iTextSharp.tool.xml.XMLWorkerHelper.GetInstance().ParseXHtml(writer, doc, msHtml, msCss);
                        }
                    }


                    doc.Close();
                }
            }
            //bytes = ms.ToArray();
            return File(ms, "application/pdf", "Test.pdf");
        }

我读过MemoryStream - 无法访问封闭的Stream,但这不是同一个场景,因为我没有使用StreamReader

编辑:仍然没有使用

    [OutputCache(NoStore = true, Duration = 0)]
    public ActionResult Run()
    {
        Byte[] bytes;
        var ms = new MemoryStream();
        try
        {
            using (var doc = new Document())
            {
                using (var writer = PdfWriter.GetInstance(doc, ms))
                {
                    writer.CloseStream = false;
                    doc.Open();
                    var example_html = @"<p>This <em>is </em><span class=""headline"" style=""text-decoration: underline;"">some</span> <strong>sample <em> text</em></strong><span style=""color: red;"">!!!</span></p>";
                    //var example_html = System.IO.File.ReadAllText(Path.Combine(Server.MapPath("~/EmailTemplates"), "LinkEmailTemplate.html"));
                    var example_css = @".headline{font-size:200%}";
                    using (var msCss = new MemoryStream(System.Text.Encoding.UTF8.GetBytes(example_css)))
                    {
                        using (var msHtml = new MemoryStream(System.Text.Encoding.UTF8.GetBytes(example_html)))
                        {
                            iTextSharp.tool.xml.XMLWorkerHelper.GetInstance().ParseXHtml(writer, doc, msHtml, msCss);
                        }
                    }
                    doc.Close();
                }
            }
            bytes = ms.ToArray();
            ms.Position = 0;
            return File(ms, "application/pdf", "Test.pdf");
        }
        catch
        {
            ms.Dispose();
            throw;
        }           
    }

Answer 1

退出操作方法后,流即关闭,或者更确切地说,using ( var ms = new MemoryStream() ) {块.

您不需要处理MemoryStream.返回的FileStreamResult对象File(ms, "application/pdf", "Test.pdf");将在渲染后处置它.实际发送流数据的代码是:

protected async override Task WriteFileAsync(HttpResponse response)
{
    var outputStream = response.Body;

    using (FileStream)
    {
        var bufferingFeature = response.HttpContext.Features.Get<IHttpBufferingFeature>();
        bufferingFeature?.DisableResponseBuffering();

        await FileStream.CopyToAsync(outputStream, BufferSize);
    }
}

您可以使用以下块替换此块:

var ms = new MemoryStream();
try
{
     //..
     //From Igor's comment. FileStreamResult won't reset the stream position itself
     ms.Position=0;
     return File(ms, "application/pdf", "Test.pdf");
}
catch
{
    ms.Dispose();
    throw;
}

确保在发生错误时丢弃流.

UPDATE

正如Igor所提到的,并且正如源代码所示,FileStreamResult不会重置流位置.你必须在打电话之前将它设置为0return File(...)

Answer 2

班级PdfWriter可能会关闭您的直播。确保将该CloseStream属性设置为 false。

接下来，您不using应该在此处使用MemoryStream，因为FileStreamResult操作结果将在发送流后负责处理该流。现在，在发送发生之前，流实际上已关闭（通过处理）。

另外，在发送文件之前，您应该将流返回到位置 0。

您可以将整个部分包装在 a 中try...catch，以便在发生错误时处理流（但 GC 最终会处理它，MemoryStream如果管理不当，所以这不是强制性的）。