c# - 新添加成员后反序列化类时出现问题

Question

我有一个简单的“可序列化”类，定义如下:

[Serializable]
public class LayoutDetails
{       
    public bool IsRefreshEnabled { get; set; }

    public string GridSettings { get; set; }

    public List<string> GroupByPropertyNames { get; set; }
}

该类已使用以下例程进行序列化:

using (var memoryStream = new MemoryStream())
{
   var dc = new DataContractSerializer(obj.GetType());
   dc.WriteObject(memoryStream, obj);

   memoryStream.Flush();

   memoryStream.Position = 0;
   StreamReader reader = new StreamReader(memoryStream);
   serializedObject = reader.ReadToEnd();
}

我尝试使用以下例程对其进行反序列化:

   var bytes = new UTF8Encoding().GetBytes(serializedObject);
   using (var stream = new MemoryStream(bytes ))
   {
      var serializer = new DataContractSerializer(type);
      var reader = XmlDictionaryReader.CreateTextReader(stream, XmlDictionaryReaderQuotas.Max);
      obj = serializer.ReadObject(reader, true);
   }

这非常有效；但是，现在，我想向类添加一个新属性 (public int? Offset { get; set; })。当我将此属性添加到类中并尝试反序列化以前序列化的实例(没有该属性)时，出现异常:

Error in line 1 position 148. 'EndElement' 'LayoutDetails' from namespace 'http://schemas.datacontract.org/2004/07/WpfApplication1' is not expected. Expecting element '_x003C_Offset_x003E_k__BackingField'.

我的第一个想法是实现 ISerialized 并使用反序列化构造函数，所以我尝试了类似的方法，但它无法按名称找到任何成员 - 而且我尝试了几种组合。 .

public LayoutDetails(SerializationInfo info, StreamingContext context)
{
   this.IsRefreshEnabled = (bool)info.GetValue("_x003C_IsRefreshEnabled_x003E_k__BackingField", typeof(bool));
   this.IsRefreshEnabled = (bool)info.GetValue("_x003C_IsRefreshEnabled_x003E_k_", typeof(bool));
   this.IsRefreshEnabled = (bool)info.GetValue("_x003C_IsRefreshEnabled_x003E", typeof(bool));
   this.IsRefreshEnabled = (bool)info.GetValue("x003C_IsRefreshEnabled_x003E", typeof(bool));
   this.IsRefreshEnabled = (bool)info.GetValue("IsRefreshEnabled", typeof(bool));
}

使用 DataContractSerializer，如何在不破坏“旧”实例上的反序列化的情况下向我的类添加新成员？

Answer 1

您可以使用新属性的支持字段，并添加属性OptionalField:

[Serializable]
public class LayoutDetails
{       
    [OptionalField]
    private int? offset;

    public bool IsRefreshEnabled { get; set; }

    public string GridSettings { get; set; }

    public List<string> GroupByPropertyNames { get; set; }

    public int? Offset
    {
        get { return offset; }
        set { offset = value; }
    }
}

如果你想设置默认值，你可以使用属性OnDeserializing向类添加一个方法:

[OnDeserializing]
private void SetOffsetDefault(StreamingContext sc)
{
    offset = 123;
}