更改XML序列化中元素的类型 [英] Changing type of element in XML Serialization

问题描述

我在XML序列化方面遇到了很大的问题。我有两个类，都需要可序列化。在继承的类中，我想更改序列化行为，以便将字符串属性序列化为复杂类型。

I am having huge problems with XML serialization. I have two classes, both need to be serializeable. In the inherited class, I would like to change the serialization behavior, so that a string property gets serialized as complex type.

public class Animal
{
    [XmlElement(ElementName = "NAME")]
    public string Name { get; set; }
    public virtual bool ShouldSerializeName() { return true; }
}

public class Cat : Animal
{
    public override bool ShouldSerializeName() { return false; }

    [XmlElement(ElementName = "NAME")]
    public NameAndType Name2 { get; set; }
}

public class NameAndType
{
    public string Name { get; set; }
    public string Type { get; set; }
}

...

var cat = new Cat {Name2 = new NameAndType {Name = "LittleCat"}};
new XmlSerializer(typeof(Cat)).Serialize(Console.Out, cat);

我尝试了不同的方法，但是我没有找到改变<$ c方式的方法$ c> NAME 元素已序列化。
在上面的示例中，我收到错误消息：

I have tried different approaches, but I didn't find a way to change how the NAME element get's serialized. With the example above, I get the error message:

名称空间中的XML元素 NAME已经存在当前范围。使用XML属性为元素指定另一个XML名称或名称空间。

推荐答案

错误是，在 XmlSerializer 代码生成，代码生成器将无法理解 Cat 上两个潜在的 NAME 元素会永远不会同时进行序列化，因此会引发异常。

The reason you get the error is that, during XmlSerializer code generation, the code generator doesn't understand that the two potential NAME elements on Cat will never be simultaneously serialized, so throws the exception.

相反，您可以应用 XmlAnyElementAttribute 到返回 XElement ，然后手动创建并返回适当的 XElement 作为层次结构中每个类的名称：

Instead, you can apply XmlAnyElementAttribute to a virtual property returning an XElement, then manually create and return an appropriate XElement for the name for each class in the hierarchy:

[XmlInclude(typeof(Cat))]
public class Animal
{
    [XmlIgnore]
    public string Name { get; set; }

    [XmlAnyElement]
    public virtual XElement XmlName
    {
        get
        {
            return Name == null ? null : new XElement("NAME", Name);
        }
        set
        {
            Name = (value == null ? null : value.Value);
        }
    }
}

public class Cat : Animal
{
    // Must be cached as per https://msdn.microsoft.com/en-us/library/system.xml.serialization.xmlserializer%28v=vs.110%29.aspx
    static XmlSerializer nameSerializer;

    static Cat()
    {
        nameSerializer = new XmlSerializer(typeof(NameAndType), new XmlRootAttribute("NAME"));
    }

    [XmlIgnore]
    public NameAndType Name2 { get; set; }

    [XmlAnyElement]
    public override XElement XmlName
    {
        get
        {
            return (Name2 == null ? null : XObjectExtensions.SerializeToXElement(Name2, nameSerializer, true));
        }
        set
        {
            Name2 = (value == null ? null : XObjectExtensions.Deserialize<NameAndType>(value, nameSerializer));
        }
    }
}

使用扩展方法：

public static class XObjectExtensions
{
    public static T Deserialize<T>(this XContainer element)
    {
        return element.Deserialize<T>(new XmlSerializer(typeof(T)));
    }

    public static T Deserialize<T>(this XContainer element, XmlSerializer serializer)
    {
        using (var reader = element.CreateReader())
        {
            object result = serializer.Deserialize(reader);
            if (result is T)
                return (T)result;
        }
        return default(T);
    }

    public static XElement SerializeToXElement<T>(this T obj)
    {
        return obj.SerializeToXElement(new XmlSerializer(obj.GetType()), true);
    }

    public static XElement SerializeToXElement<T>(this T obj, XmlSerializer serializer, bool omitStandardNamespaces)
    {
        var doc = new XDocument();
        using (var writer = doc.CreateWriter())
        {
            XmlSerializerNamespaces ns = null;
            if (omitStandardNamespaces)
                (ns = new XmlSerializerNamespaces()).Add("", ""); // Disable the xmlns:xsi and xmlns:xsd lines.
            serializer.Serialize(writer, obj, ns);
        }
        var element = doc.Root;
        if (element != null)
            element.Remove();
        return element;
    }
}

对于 List < ; Animal> ，生成如下所示的XML：

Which, for a List<Animal>, produces XML like this:

<ArrayOfAnimal xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <Animal>
        <NAME>duck</NAME>
    </Animal>
    <Animal xsi:type="Cat">
        <NAME>
            <Name>Smokey</Name>
            <Type>Siamese</Type>
        </NAME>
    </Animal>
</ArrayOfAnimal>

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