.NET 6下XML反序列化为Parameters对象报错，原.NET Core 2.2正常

输入XML字符串：

<ActivationRequest xmlns="http://schemas.datacontract.org/2004/07/DataLayer.Models" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
    <Key>key</Key>
    <Edition i:nil="true"/>
    <HardwareId>542D</HardwareId>
    <IntelliLockFlags>BIOS CPU</IntelliLockFlags>
    <MachineName>nikolas</MachineName>
    <Product>studio</Product>
    <UseMacHID>false</UseMacHID>
    <Version xmlns:a="http://schemas.datacontract.org/2004/07/System">
        <a:_Build>88</a:_Build>
        <a:_Major>6</a:_Major>
        <a:_Minor>4</a:_Minor>
        <a:_Revision>0</a:_Revision>
    </Version>
</ActivationRequest>

反序列化方法：

public static Parameters DeserializeFromXml<T>(this string xml)
{
    using (var stream = new MemoryStream())
    {
        byte[] data = Encoding.UTF8.GetBytes(xml);
        stream.Write(data, 0, data.Length);
        stream.Position = 0;

        var deserializer = new DataContractSerializer(typeof(Parameters));
        return deserializer.ReadObject(stream) as Parameters; // error
    }
}

模型类定义：

public class Parameters
{
    public string Key { get; set; }
    public string HardwareId { get; set; }
    public string Product { get; set; }
    public Version Version { get; set; }
    public bool UseMacHID { get; set; }
    public LockFlags IntelliLockFlags { get; set; }
    public string MachineName { get; set; }
}

[Flags]
public enum LockFlags
{
    Empty = 0,
    BIOS = 1,
    CPU = 2
}

代码在.NET Core 2.2中正常运行，升级到.NET 6后抛出错误：

Error in line 1 position 144. Expecting element 'ActivationParameters' from namespace 'http://schemas.datacontract.org/2004/07/DataLayer.NetStandard.BusinessLayer.Activation'.. Encountered 'Element' with name 'ActivationRequest', namespace 'http://schemas.datacontract.org/2004/07/DataLayer.Models'.

.NET Core 2.2到.NET 6的版本迭代中，DataContractSerializer的默认行为发生了变更：

• 旧版本中可能自动兼容了类型名称、命名空间的不匹配，或默认命名空间推断逻辑更宽松
• 新版本中序列化器会严格校验根元素的名称和命名空间，当前代码中序列化器默认推断出的Parameters类对应元素名和命名空间，与XML中的ActivationRequest及目标命名空间完全不匹配，因此触发错误

方案1：给模型类添加显式特性匹配XML结构 #

通过DataContract和DataMember特性，直接指定模型类对应的XML根元素名称、命名空间，同时给枚举添加EnumMember确保字符串值能被正确解析：

[DataContract(Name = "ActivationRequest", Namespace = "http://schemas.datacontract.org/2004/07/DataLayer.Models")]
public class Parameters
{
    [DataMember]
    public string Key { get; set; }
    [DataMember]
    public string HardwareId { get; set; }
    [DataMember]
    public string Product { get; set; }
    [DataMember]
    public Version Version { get; set; }
    [DataMember]
    public bool UseMacHID { get; set; }
    [DataMember(Name = "IntelliLockFlags")]
    public LockFlags IntelliLockFlags { get; set; }
    [DataMember]
    public string MachineName { get; set; }
}

[Flags]
[DataContract]
public enum LockFlags
{
    [EnumMember]
    Empty = 0,
    [EnumMember]
    BIOS = 1,
    [EnumMember]
    CPU = 2
}

方案2：修改序列化器初始化参数，指定根元素信息 #

无需修改模型类，在创建DataContractSerializer时显式传入XML根元素的名称和命名空间：

public static Parameters DeserializeFromXml<T>(this string xml)
{
    using (var stream = new MemoryStream())
    {
        byte[] data = Encoding.UTF8.GetBytes(xml);
        stream.Write(data, 0, data.Length);
        stream.Position = 0;

        // 显式指定根元素名称与命名空间，匹配XML内容
        var deserializer = new DataContractSerializer(
            typeof(Parameters),
            "ActivationRequest",
            "http://schemas.datacontract.org/2004/07/DataLayer.Models");
        return deserializer.ReadObject(stream) as Parameters;
    }
}

方案3：额外处理枚举的空格分隔值解析 #

如果XML中IntelliLockFlags的空格分隔枚举值（BIOS CPU）无法被正确解析，可以通过序列化器配置强化枚举支持：

public static Parameters DeserializeFromXml<T>(this string xml)
{
    using (var stream = new MemoryStream())
    {
        byte[] data = Encoding.UTF8.GetBytes(xml);
        stream.Write(data, 0, data.Length);
        stream.Position = 0;

        var settings = new DataContractSerializerSettings
        {
            UseEnumMemberNames = true
        };

        var deserializer = new DataContractSerializer(
            typeof(Parameters),
            "ActivationRequest",
            "http://schemas.datacontract.org/2004/07/DataLayer.Models",
            null,
            int.MaxValue,
            false,
            true,
            null,
            settings);
        return deserializer.ReadObject(stream) as Parameters;
    }
}

内容的提问来源于stack exchange，提问作者lucianobonde