c# 使用 + XmlWriter.Create = "Cannot access a closed Stream."

Question

为什么会这样:

using (var ms = new MemoryStream())
{
    using (var dummy = new StreamWriter(ms))
    {
        var sw = new StreamWriter(ms);
        sw.WriteLine("Hello World");
        sw.Flush();
        using (StreamReader rdr = new StreamReader(ms))
        {
            ms.Position = 0;
            textBoxExc.Text = rdr.ReadToEnd();
        }
    }
}

但这不起作用(“无法访问已关闭的流。”):唯一的区别是 var dummy = XmlWriter.Create(ms) 而不是 var dummy = new StreamWriter(ms)

using (var ms = new MemoryStream())
{
    using (var dummy = XmlWriter.Create(ms))
    {
        var sw = new StreamWriter(ms);
        sw.WriteLine("Hello World");
        sw.Flush();
        using (StreamReader rdr = new StreamReader(ms))
        {
            ms.Position = 0;
            textBoxExc.Text = rdr.ReadToEnd();
        }
    }
}

堆栈跟踪:

System.ObjectDisposedException was unhandled by user code
  Message=Cannot access a closed Stream.
  ObjectName=""
  StackTrace:
       w System.IO.__Error.StreamIsClosed()
       w System.IO.MemoryStream.Write(Byte[] buffer, Int32 offset, Int32 count)
       w System.Xml.XmlUtf8RawTextWriter.FlushBuffer()
       w System.Xml.XmlUtf8RawTextWriter.Flush()
       w System.Xml.XmlWellFormedWriter.Close()
       w System.Xml.XmlWriter.Dispose(Boolean disposing)
       w System.Xml.XmlWriter.Dispose()
       w SerializeTest.MainPage.buttonExc_Click(Object sender, RoutedEventArgs e)
       w System.Windows.Controls.Primitives.ButtonBase.OnClick()
       w System.Windows.Controls.Button.OnClick()
       w System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
       w System.Windows.Controls.Control.OnMouseLeftButtonUp(Control ctrl, EventArgs e)
       w MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName)
  InnerException: 

这也不起作用(同样的错误):

using (var ms = new MemoryStream())
{
     using (var writer = XmlWriter.Create(ms))
    {
        var serializer = new DataContractSerializer(typeof(T));
        serializer.WriteObject(writer, objectToSave);
        writer.Flush();
        ms.Position = 0;
        using (StreamReader rdr = new StreamReader(ms))
        {
            return rdr.ReadToEnd();
        }
    }
}

堆栈跟踪:

System.ObjectDisposedException was unhandled by user code
  Message=Cannot access a closed Stream.
  ObjectName=""
  StackTrace:
       w System.IO.__Error.StreamIsClosed()
       w System.IO.MemoryStream.Write(Byte[] buffer, Int32 offset, Int32 count)
       w System.Xml.XmlUtf8RawTextWriter.FlushBuffer()
       w System.Xml.XmlUtf8RawTextWriter.Flush()
       w System.Xml.XmlWellFormedWriter.Close()
       w System.Xml.XmlWriter.Dispose(Boolean disposing)
       w System.Xml.XmlWriter.Dispose()
       w SerializeTest.SerializeToStringTest[T](T objectToSave)
       w SerializeTest.MainPage.button2A_Click(Object sender, RoutedEventArgs e)
       w System.Windows.Controls.Primitives.ButtonBase.OnClick()
       w System.Windows.Controls.Button.OnClick()
       w System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
       w System.Windows.Controls.Control.OnMouseLeftButtonUp(Control ctrl, EventArgs e)
       w MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName)
  InnerException: 

但这有效(唯一的区别是 StreamReader w/o using):

using (var ms = new MemoryStream())
{
     using (var writer = XmlWriter.Create(ms))
    {
        var serializer = new DataContractSerializer(typeof(T));
        serializer.WriteObject(writer, objectToSave);
        writer.Flush();
        ms.Position = 0;
        StreamReader rdr = new StreamReader(ms);
        return rdr.ReadToEnd();
    }
}

Answer 1

只需将从 MemoryStream block 的读取移动到一个级别并写入它。

using (var ms = new MemoryStream())
{
     using (var writer = XmlWriter.Create(ms))
    {
        var serializer = new DataContractSerializer(typeof(T));
        serializer.WriteObject(writer, objectToSave);
        writer.Flush();
        ms.Position = 0;        
    }
    using (StreamReader rdr = new StreamReader(ms))
    {
        return rdr.ReadToEnd();
    }
}