c# - 序列化异常 : "Type\...\in assembly\...\is not marked as serializable" appears when I try to serialize ObservableCollection

Question

在用作并行下载管理器的双工 WCF 服务中，我有一个显示每个下载状态的下载器类和一个包含下载器实例的 ObservableCollection。当我尝试通过 BinaryFormatter 序列化 ObservableCollection 时，我得到 SerializationException 消息:“Type\System.Net.ConnectStream\in assembly\System.Version 4.0.0.0, Culture=neutral, PublicKey Token=b77a5c561934e089\is not marked as serializable”。下面是 Downloader 类的精简版:

[Serializable()]
public class Downloader
{
     /// <summary>
     /// "Download status changed" event.
     /// </summary>
     [field: NonSerialized()]
     public event EventHandler<InServiceHandledDownloadStatusChangedEventArgs>    InServiceHandledDownloadStatusChanged;

     /// <summary>
     /// URL of downloaded resource.
     /// </summary>
     private String _targetUrl;  

     /// <summary>
     /// Path to save downloaded data on local drive.
     /// </summary>
     private String _pathToSave;

     /// <summary>
     /// The number of bytes downloaded from internet resource.
     /// </summary>
     private Int64 _downloadedBytesQuantity = 0;

     /// <summary>
     /// Current status of downloading ("Await", "Running", "Completed").
     /// </summary>
     private String _status = "Added";

     /// <summary>
     /// Task that performs download.
     /// </summary>
     [NonSerialized()]
     public Task TaskPerformingDownload;

     /// <summary>
     /// The source of cancellation token for cancelling of TaskPerformingDownload.
     /// </summary>
     [NonSerialized()]
     public CancellationTokenSource CancelDownloadTokenSource;

     /// <summary>
     ///  Gets or sets stream to read downloaded data from internet.
     /// </summary>
     public Stream ReadСontentStream { get; set; }

     /// <summary>
     /// Gets or sets stream to write downloaded data to local drive.
     /// </summary>
     public Stream SaveСontentStream { get; set; }

     /// <summary>
     /// This method executes in TaskPerformingDownload and performs downloading.
     /// of a resource from internet.
     /// </summary>
     /// <param name="p_CancellationToken">Cancellation Token</param>
     public void PerformDownload(Object p_CancellationToken)
     {
         try
         {
             // Get cancellation token.
             CancellationToken cancellationToken = (CancellationToken)p_CancellationToken;
             // Check was the task canceled?
             cancellationToken.ThrowIfCancellationRequested();
             . . . . . . . . 
             HttpWebRequest webResourceRequest = (HttpWebRequest)WebRequest.Create(TargetUrl);
             HttpWebResponse webResourceResponse = (HttpWebResponse)webResourceRequest.GetResponse();
             this.ReadСontentStream = webResourceResponse.GetResponseStream();
             this.SaveСontentStream = new FileStream(this.PathToSave, FileMode.Create, FileAccess.Write, FileShare.None);
             int bytesReceivedInChank = 0;
             byte[] downloadBuffer = new byte[2048];

             // The downloading loop.
             while ((bytesReceivedInChank = this.ReadСontentStream.Read(downloadBuffer, 0, downloadBuffer.Length)) > 0)
             {
                  if (cancellationToken.IsCancellationRequested)
                    cancellationToken.ThrowIfCancellationRequested();
                  this.SaveСontentStream.Write(downloadBuffer, 0, bytesReceivedInChank);
                  . . . . . . . .
             }
        }
        catch(Exception){. . . .}
        finally
        {
            if (this.ReadСontentStream != null)
            {
                this.ReadСontentStream.Close();
                this.ReadСontentStream.Dispose();
            }
            if (this.SaveСontentStream != null)
            {
                this.SaveСontentStream.Close();
                this.SaveСontentStream.Dispose();
            }
        }
     }
}

TaskPerformingDownload 成员是执行一次下载的 TPL 任务。它是从 StartDownload() 契约(Contract)方法开始的，当客户端要求这样做时，WCF 服务会调用该方法。在此任务中执行 PerformDownload 方法。 WCF 服务创建与必须执行的下载一样多的下载器实例。每次下载一个下载器实例。带有消息的 SerializationException 异常:“Type\System.Net.ConnectStream\in assembly\System.Version 4.0.0.0, Culture=neutral, PublicKey Token=b77a5c561934e089\is not marked as serializable”仅当我尝试序列化 ObservableCollection 时才会发生下载。下载完成后，其任务(TaskPerformingDownload 成员)也已完成其工作，不再执行。我尝试在已完成的下载中处理任务，但它没有帮助并且 SerializationException 异常仍然存在。但是，如果 ObservableCollection 中只有新的下载，那么尚未运行的下载(因此此下载的 TaskPerformingDownload 成员尚未运行)，在这种情况下，ObservableCollection 序列化很好，没有任何异常或错误。你能告诉我为什么会出现这种情况吗？这对我来说非常重要。

Answer 1

您正在尝试序列化一个Stream。这是灾难的根源:流不是数据桶——它们是管道；它们很少以任何有意义的方式序列化，如果有的话。我的建议很简单:不要那样做。事实上，根本不要尝试序列化 Downloader ；您应该序列化数据，而不是实现状态。创建一个单独的模型，仅用于序列化，其中包含您要以最简单、最明显的方式存储的数据。如果你想序列化一个二进制请求/响应:byte[]。等等。

另外:出于多种原因，我强烈建议不要在几乎所有场景中使用 BinaryFormatter。