c# - 我可以在不实现 IXmlSerializable 的情况下为 XmlSerializer 提供自定义序列化吗？

Question

我们正在使用 XmlSerializer，我想为某些类提供自定义序列化。但是，我并不总是能够修改相关类的源代码，否则我只能让它实现 IXmlSerializable。有什么办法吗？

Answer 1

这是代理反序列化助手的一个简单示例:

给定一个我们无法在类级别直接控制序列化的类型:

public sealed class Class //contrived example
{
    public string Property {get;set;}
}

我们需要反序列化的 xml:

<Class>
  <Property>Value</Property>
</Class>

您可以创建一个代理类型来手动处理目标类型的反序列化过程，如下所示:

[XmlRoot("Class")] // <-- Very important
public sealed class ClassSerializerProxy : IXmlSerializable
{
    public Class ClassValue {get;set;}

    public System.Xml.Schema.XmlSchema GetSchema(){return null;}
    public void WriteXml(System.Xml.XmlWriter writer){}

    public void ReadXml(System.Xml.XmlReader reader)
    {
        var x = XElement.ReadFrom(reader) as XElement;
        this.ClassValue = new Class();
        //again this is a simple contrived example
        this.ClassValue.Property = x.XPathSelectElement("Property").Value;
    }
}

用法是:

void Main()
{
    // get the xml value somehow
    var xdoc= XDocument.Parse(@"<Class><Property>Value</Property></Class>");

    // deserialize the xml into the proxy type
    var proxy = Deserialize<ClassSerializerProxy>(xdoc);

    // read the resulting value
    var value = proxy.ClassValue;
}

public object Deserialize(XDocument xmlDocument, Type DeserializeToType)
{
    XmlSerializer xmlSerializer = new XmlSerializer(DeserializeToType);
    using (XmlReader reader = xmlDocument.CreateReader())
        return xmlSerializer.Deserialize(reader);
}

现在加入一些泛型和扩展方法，我们可以为最终(异常处理除外)版本稍微清理一下调用站点:

用法:

void Main()
{
    var xml = @"<Class><Property>Value</Property></Class>";

    var value = xml.DeserializeWithProxy<ClassSerializerProxy,Class>();

    value.Dump();
}

您的实例类型:

public sealed class Class
{
    public string Property {get;set;}
}

代理类型必须实现的接口(interface)

public interface ISerializerProxy<TInstanceType> where TInstanceType : class
{
    TInstanceType Value { get; }
}

示例代理现在实现了新接口(interface)

[XmlRoot("Class")]
public sealed class ClassSerializerProxy : IXmlSerializable, ISerializerProxy<Class>
{
    public Class Value {get;set;}

    public System.Xml.Schema.XmlSchema GetSchema(){return null;}
    public void WriteXml(System.Xml.XmlWriter writer){}

    public void ReadXml(System.Xml.XmlReader reader)
    {
        var x = XElement.ReadFrom(reader) as XElement;
        this.Value = new Class();
        this.Value.Property = x.XPathSelectElement("Property").Value;
    }
}

反序列化方法现在是 string 的扩展方法，可以与任何代理类型一起使用。

public static class ExtensionMethods
{
    public static TInstanceType DeserializeWithProxy<TProxyType,TInstanceType>(this string xml) 
        where TProxyType : ISerializerProxy<TInstanceType> 
        where TInstanceType : class
    {
        using (XmlReader reader = XDocument.Parse(xml).CreateReader())
        {
            var xmlSerializer = new XmlSerializer(typeof(TProxyType));
            return (xmlSerializer.Deserialize(reader) as ISerializerProxy<TInstanceType>).Value;
        }
    }
}