c# – 为什么我在这里“无法访问封闭的流”？

发布时间：2020-12-15 04:29:56 所属栏目：百科来源：网络整理

导读：堆栈跟踪看起来像 [ObjectDisposedException: Cannot access a closed Stream.] System.IO.__Error.StreamIsClosed() +53 System.IO.MemoryStream.Read(Byte[] buffer,Int32 offset,Int32 count) +11411219 System.Web.Mvc.FileStreamResult.WriteFile(HttpR

堆栈跟踪看起来像

[ObjectDisposedException: Cannot access a closed 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,msHtml,msCss);
                        }
                    }


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

我读过MemoryStream – Cannot access a closed Stream,但那不是同一个场景,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,msCss);
                        }
                    }
                    doc.Close();
                }
            }
            bytes = ms.ToArray();
            ms.Position = 0;
            return File(ms,"Test.pdf");
        }
        catch
        {
            ms.Dispose();
            throw;
        }           
    }

解决方法

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

您不需要处理MemoryStream. File返回的FileStreamResult对象(ms,“application / pdf”,“Test.pdf”);将dispose it after rendering.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,"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.在调用返回文件(…)之前,你必须将它设置为0

（编辑：李大同）

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