问题描述： 当使用AddXmlDataContractSerializer方法序列化包含子资源的对象时，可能会遇到序列化失败的问题。例如，以下代码示例将一个Order对象序列化为XML字符串：

[DataContract]
public class Order
{
    [DataMember]
    public int Id { get; set; }

    [DataMember]
    public List Items { get; set; }
}

[DataContract]
public class OrderItem
{
    [DataMember]
    public string Name { get; set; }
}

var order = new Order
{
    Id = 1,
    Items = new List
    {
        new OrderItem { Name = "Product 1" },
        new OrderItem { Name = "Product 2" }
    }
};

var serializer = new DataContractSerializer(typeof(Order), new DataContractSerializerSettings
{
    PreserveObjectReferences = true,
    KnownTypes = new[] { typeof(OrderItem) }
});

var xmlSettings = new XmlWriterSettings
{
    OmitXmlDeclaration = true,
    NamespaceHandling = NamespaceHandling.OmitDuplicates
};

using (var buffer = new MemoryStream())
{
    using (var xmlWriter = XmlWriter.Create(buffer, xmlSettings))
    {
        serializer.WriteObject(xmlWriter, order);
    }

    var xml = Encoding.UTF8.GetString(buffer.ToArray());
    Console.WriteLine(xml);
}

当运行以上代码时，可能会遇到以下异常：

System.Runtime.Serialization.SerializationException: 类型 “System.Collections.Generic.List`1[[ConsoleApp1.OrderItem, ConsoleApp1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]”（用作根）在序列化时引用了类型 “ConsoleApp1.OrderItem” 的循环引用。

〔 要解决此问题，可以将AddXmlSerializer方法替换为AddDataContractSerializer方法。以下是修改后的代码示例：

var host = new ServiceHost(typeof(MyService));
var binding = new BasicHttpBinding();
var endpoint = host.AddServiceEndpoint(typeof(IMyService), binding, "http://localhost/MyService");

var serializerBehavior = new DataContractSerializerOperationBehavior(endpoint.Contract.Operations.FirstOrDefault());

要解决此问题，可以将AddXmlSerializer方法替换为AddDataContractSerializer方法。以下是修改后的代码示例：

```csharp
var host = new ServiceHost(typeof(MyService));
var binding = new BasicHttpBinding();
var endpoint = host.AddServiceEndpoint(typeof(IMyService), binding, "http://localhost/MyService");

var serializerBehavior = new DataContractSerializerOperationBehavior(endpoint.Contract.Operations.FirstOrDefault());