C# DataContractSerializer 不调用我的构造函数？
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DataContractSerializer doesn't call my constructor?
提问by Thomas Levesque
I just realized something crazy, which I assumed to be completely impossible : when deserializing an object, the DataContractSerializer doesn't call the constructor!
我刚刚意识到一些疯狂的事情，我认为这是完全不可能的：反序列化对象时，DataContractSerializer 不会调用构造函数！
Take this class, for instance :
以这个类为例：
[DataContract]
public class Book
{
public Book()
{ // breakpoint here
}
[DataMember(Order = 0)]
public string Title { get; set; }
[DataMember(Order = 1)]
public string Author { get; set; }
[DataMember(Order = 2)]
public string Summary { get; set; }
}
When I deserialize an object of that class, the breakpoint is not hit. I have absolutely no idea how it is possible, since it is the only constructor for this object !
当我反序列化那个类的对象时，断点没有被命中。我完全不知道这是怎么可能的，因为它是这个对象的唯一构造函数！
I assumed that perhaps an additional constructor was generated by the compiler because of the DataContractattribute, but I couldn't find it through reflection...
我假设编译器可能因为DataContract属性而生成了一个额外的构造函数，但是我无法通过反射找到它......
So, what I'd like to know is this : how could an instance of my class be created without the constructor being called ??
所以，我想知道的是：如何在不调用构造函数的情况下创建我的类的实例？
NOTE: I know that I can use the OnDeserializingattribute to initialize my object when deserialization begins, this is not the subject of my question.
注意：我知道我可以OnDeserializing在反序列化开始时使用该属性来初始化我的对象，这不是我的问题的主题。
采纳答案by Marc Gravell
DataContractSerializer(like BinaryFormatter) doesn't use anyconstructor. It creates the object as empty memory.
DataContractSerializer（如BinaryFormatter）不使用任何构造函数。它将对象创建为空内存。
For example:
例如：
Type type = typeof(Customer);
object obj = System.Runtime.Serialization.
FormatterServices.GetUninitializedObject(type);
The assumption is that the deserialization process (or callbacks if necessary) will fully initialize it.
假设是反序列化过程（或必要时回调）将完全初始化它。
回答by BasvdL
There are some scenario's that wouldn't be possible without this behavior. Think of the following:
如果没有这种行为，有些情况是不可能的。考虑以下几点：
1) You have an object that has one constructor that sets the new instance to an "initialized" state. Then some methods are called on that instance, that bring it in a "processed" state. You don't want to create new objects having the "processed" state, but you still want de serialize / deserialize the instance.
1) 您有一个对象，该对象具有一个构造函数，该构造函数将新实例设置为“已初始化”状态。然后在该实例上调用一些方法，使其处于“已处理”状态。您不想创建具有“已处理”状态的新对象，但您仍然希望对实例进行反序列化/反序列化。
2) You created a class with a private constructor and some static properties to control a small set of allowed constructor parameters. Now you can still serialize / deserialize them.
2) 您创建了一个带有私有构造函数和一些静态属性的类来控制一小组允许的构造函数参数。现在您仍然可以序列化/反序列化它们。
XmlSerializer has the behavior you expected. I have had a some problems with the XmlSerializer because it DOES need a default constructor. Related to that, sometimes it makes sense to have private property setters. But the XmlSerializer also needs public getter and setter on properties in order to serialize / deserialize.
XmlSerializer 具有您预期的行为。我在使用 XmlSerializer 时遇到了一些问题，因为它确实需要一个默认构造函数。与此相关，有时拥有私有财产设定者是有意义的。但是 XmlSerializer 还需要属性上的公共 getter 和 setter，以便序列化/反序列化。
I think of the DataContractSerializer / BinaryFormatter behavior like suspending the state of an instance during serialization and resuming during deserialization. In other words, the instances are not “constructed” but “restored” to an earlier state.
我想到了 DataContractSerializer / BinaryFormatter 行为，例如在序列化期间暂停实例的状态并在反序列化期间恢复。换句话说，实例不是“构造”而是“恢复”到较早的状态。
As you already mentioned, the [OnDeserializing] attribute makes it possible to keep non serialized data in sync.
正如您已经提到的，[OnDeserializing] 属性可以使非序列化数据保持同步。
