c＃using + XmlWriter.Create =「無法訪問封閉的流。」

Question

爲什麼這個工程：（ 「無法訪問已關閉的流」）

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(); 
     } 
    } 
} 

但這不起作用： 唯一的區別是var dummy = XmlWriter.Create(ms)代替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(); 
     } 
    } 
} 

堆棧跟蹤：

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: 

而且這不工作（同樣的錯誤）：

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(); 
     } 
    } 
} 

堆棧跟蹤：

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: 

但這個工程（唯一的區別是StreamReader瓦特/ 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

，你能不能給我們異常的完整堆棧跟蹤？我的第一個猜測是XmlWriter仍試圖將XmlWriter的Dispose()方法中訪問流。

在你的第二個和第四個代碼示例您將StreamReader在使用塊。這導致StreamReader的Dispose()方法的調用在該塊的結束。此方法關閉閱讀器和基礎流。在此之後，XmlWriter的Dispose()方法無法再訪問該流。

更新： 基於stackstrace看來我是對的。該Dispose()方法調用Close()，這反過來又要刷新的已關閉流。這看起來像一個錯誤，因爲應該沒有什麼可以刷新。

你已經給瞭解決方案：XmlWriter的處置前不關閉的MemoryStream。

（我假設你知道，使用塊隱含部署的使用對象，並設置一StreamReader或StreamWriter隱含部署（並關閉）底層流。）

Answer 2

剛剛擺脫的MemoryStream塊寫上一個與寫入它的水平。

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(); 
    } 
}