C# 序列化一个没有无参数构造函数的类
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C# serialize a class without a parameterless constructor
提问by Roger Bacon
I'm implementing a factory pattern for 3 different cryptography classes. The factory will determine which one to create and then get a serialized instance of the correct class from a database and return it to the requester.
Right now I'm working on serializing the classes to store them in the database. I'm writing one for a PGP cryptography class called BouncyCastle. I can create the class and the keys from files but when I try to serialize it, it says that the two member variables, which are objects of class PgpPublicKey, and PgpPrivateKey, cannot be serialized because they do not have parameterless constructors.
我正在为 3 个不同的密码学类实现工厂模式。工厂将决定创建哪一个，然后从数据库中获取正确类的序列化实例并将其返回给请求者。现在我正在对类进行序列化以将它们存储在数据库中。我正在为一个名为BouncyCastle. 我可以从文件创建类和键，但是当我尝试序列化它时，它说两个成员变量，它们是 classPgpPublicKey和 的对象PgpPrivateKey，无法序列化，因为它们没有无参数构造函数。
public void createdBouncyFromFiles()
{
var bc = new BouncyCastle("C:\TestFiles\BouncyPublicKey.txt", "C:\TestFiles\BouncyPrivateKey.txt", "Password1");
var xmlSerializer = new XmlSerializer(bc.GetType());
var textWriter = new StringWriter();
xmlSerializer.Serialize(textWriter, bc);
var theSerializedClass = textWriter.ToString();
}
The class has two member variables that are the problem.
该类有两个成员变量是问题所在。
public class BouncyCastle : ICryptographyProvider
{
public PgpPublicKey m_publicKey;
public PgpPrivateKey m_privateKey;
public string m_passPhrase;
// cut out the irelevant parts
This is the public key class. No parameterless constructor.
这是公钥类。没有无参数的构造函数。
public class PgpPublicKey
{
public PgpPublicKey(PublicKeyAlgorithmTag algorithm, AsymmetricKeyParameter pubKey, DateTime time);
// cut other methods
}
采纳答案by Jamby
Any Serializer Class need a parameterless constructor because, while deserializing it create an empty new instance, then it copies every public property taken from seialized data.
任何序列化器类都需要一个无参数构造函数，因为在反序列化它时会创建一个空的新实例，然后它会复制从序列化数据中获取的每个公共属性。
You can easily make the constructor private, if you want to avoid to create it without parameters.
如果您想避免在没有参数的情况下创建它，您可以轻松地将构造函数设为私有。
EX:
前任：
public class PgpPublicKey
{
public PgpPublicKey(PublicKeyAlgorithmTag algorithm, AsymmetricKeyParameter pubKey, DateTime time);
private PgpPublicKey();
// cut other methods
}
回答by Magnum
Yes, the XmlSerializer requiresa parameterless constructor to exist in order for the serialization to work.
是的，XmlSerializer需要存在无参数构造函数才能使序列化工作。
From the following answer: Why XML-Serializable class need a parameterless constructor
来自以下答案：Why XML-Serializable class need a parameterless constructor
During an object's de-serialization, the class responsible for de-serializing an object creates an instance of the serialized class and then proceeds to populate the serialized fields and properties only after acquiring an instance to populate.
You can make your constructor private or internal if you want, just so long as its parameterless.
在对象的反序列化期间，负责反序列化对象的类创建序列化类的实例，然后仅在获取要填充的实例后才继续填充序列化的字段和属性。
如果需要，您可以将构造函数设为私有或内部，只要它是无参数的。
回答by Peter Ivan
Are PgpPublicKeyand PgpPrivateKeyclasses defined by you? Simply add parameterless constructors to them.
是否PgpPublicKey和PgpPrivateKey班由你定义的？只需向它们添加无参数构造函数即可。
They can be private if you don't want to make them accessible from outside. The deserializer can still access them.
如果您不想从外部访问它们，它们可以是私有的。解串器仍然可以访问它们。
回答by alexkovelsky
DataContractSerializer does not require parameterless constructor. What it instead requires are special attributes of class.
DataContractSerializer 不需要无参数构造函数。相反，它需要的是类的特殊属性。
回答by Basalat Raja
For anyone who is still looking a few years later, the answer is now FormatterServices.GetUninitializedObject. Be careful with it, as this is just a piece of memory set to all nulls and zeros and if a field in the object's default value is something other than zero, it might be set wrong: "Because the new instance of the object is initialized to zero and no constructors are run, the object might not represent a state that is regarded as valid by that object."
对于几年后仍在寻找的人来说，现在的答案是 FormatterServices.GetUninitializedObject。小心它，因为这只是一块设置为所有空值和零的内存，如果对象默认值中的字段不是零，则可能设置错误：“因为对象的新实例已初始化为零并且没有运行构造函数，则该对象可能不代表该对象认为有效的状态。”
