C# 未知类型的自定义 Xml 序列化
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原文地址: http://stackoverflow.com/questions/1075860/
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Custom Xml Serialization of Unknown Type
提问by Ian
I'm attempting to deserialize a custom class via the XmlSerializer and having a few problems, in the fact that I don't know the type that I'm going to be deserializing (it's pluggable) and I'm having difficulty determining it.
我正在尝试通过 XmlSerializer 反序列化自定义类，但遇到了一些问题，因为我不知道要反序列化的类型（它是可插入的），而且我很难确定它。
I found this postwhich looks similar but can't quite get it to work with my approach because I need to deserialize an interface which is XmlSerializable.
我发现这篇文章看起来很相似，但不能完全使用我的方法，因为我需要反序列化一个 XmlSerializable 接口。
What I've currently got is of the form. Note that I expect and need to be able to handle both class A and class B to be implemented via a plugin. So if I can avoid using the IXmlSerializable (which I don't think I can) then that would be great.
我目前得到的是形式。请注意，我期望并且需要能够处理通过插件实现的 A 类和 B 类。因此，如果我可以避免使用 IXmlSerializable（我认为我不能），那就太好了。
The ReadXml for A is what I'm stuck on. However if there are other changes that I can make to improve the system then I'm happy to do so.
A 的 ReadXml 是我所坚持的。但是，如果我可以进行其他更改以改进系统，那么我很乐意这样做。
public class A : IXmlSerializable
{
public IB MyB { get; set;}
public void ReadXml(System.Xml.XmlReader reader)
{
// deserialize other member attributes
SeekElement(reader, "MyB");
string typeName = reader.GetAttribute("Type");
// Somehow need to the type based on the typename. From potentially
//an external assembly. Is it possible to use the extra types passed
//into an XMlSerializer Constructor???
Type bType = ???
// Somehow then need to deserialize B's Members
// Deserialize X
// Deserialize Y
}
public void WriteXml(System.Xml.XmlWriter writer)
{
// serialize other members as attributes
writer.WriteStartElement("MyB");
writer.WriteAttributeString("Type", this.MyB.GetType().ToString());
this.MyB.WriteXml(writer);
writer.WriteEndElement();
}
private void SeekElement(XmlReader reader, string elementName)
{
ReaderToNextNode(reader);
while (reader.Name != elementName)
{
ReaderToNextNode(reader);
}
}
private void ReaderToNextNode(XmlReader reader)
{
reader.Read();
while (reader.NodeType == XmlNodeType.Whitespace)
{
reader.Read();
}
}
}
public interface IB : IXmlSerializable
{
}
public class B : IB
{
public void ReadXml(XmlReader reader)
{
this.X = Convert.ToDouble(reader.GetAttribute("x"));
this.Y = Convert.ToDouble(reader.GetAttribute("y"));
}
public void WriteXml(XmlWriter writer)
{
writer.WriteAttributeString("x", this.X.ToString());
writer.WriteAttributeString("y", this.Y.ToString());
}
}
NOTE : Updated as I realised B was supposed to use interface IB. Sorry for slightly wrong question.
注意：当我意识到 B 应该使用接口 IB 时更新。对不起，我的问题有点错误。
采纳答案by John Saunders
To create an instance from a string, use one of the overloads of Activator.CreateInstance. To just get a type with that name, use Type.GetType.
要从字符串创建实例，请使用 Activator.CreateInstance 的重载之一。要获取具有该名称的类型，请使用 Type.GetType。
回答by Shea
I'd use xpath to quickly figure out whether the input xml contains class A or class B. Then deserialize it based on that.
我会使用 xpath 快速确定输入的 xml 是否包含 A 类或 B 类。然后根据它反序列化它。
回答by Thomas Levesque
I don't think you need to implement IXmlSerializable...
我认为你不需要实施IXmlSerializable......
Since you don't know the actual types before runtime, you can dynamically add attribute overrides to the XmlSerializer. You just need to know the list of types that inherit from A. For instance, if you use A as a property of another class :
由于您在运行前不知道实际类型，因此您可以向 XmlSerializer 动态添加属性覆盖。您只需要知道从 A 继承的类型列表。例如，如果您使用 A 作为另一个类的属性：
public class SomeClass
{
public A SomeProperty { get; set; }
}
You can dynamically apply XmlElementAttributes for each derived type to that property :
您可以将XmlElementAttribute每个派生类型的 s动态应用到该属性：
XmlAttributes attr = new XmlAttributes();
var candidateTypes = from t in AppDomain.CurrentDomain.GetAssemblies().SelectMany(a => a.GetTypes())
where typeof(A).IsAssignableFrom(t) && !t.IsAbstract
select t;
foreach(Type t in candidateTypes)
{
attr.XmlElements.Add(new XmlElementAttribute(t.Name, t));
}
XmlAttributeOverrides overrides = new XmlAttributeOverrides();
overrides.Add(typeof(SomeClass), "SomeProperty", attr);
XmlSerializer xs = new XmlSerializer(typeof(SomeClass), overrides);
...
This is just a very basic example, but it shows how to apply XML serialization attributes at runtime when you can't do it statically.
这只是一个非常基本的示例，但它展示了当您无法静态执行时如何在运行时应用 XML 序列化属性。
