There is some magic going on with WCF deserialization. How does it instantiate an instance of the data contract type without calling its constructor?
For example, consider this data contract:
[DataContract]
public sealed class CreateMe
{
[DataMember] private readonly string _name;
[DataMember] private readonly int _age;
private readonly bool _wasConstructorCalled;
public CreateMe()
{
_wasConstructorCalled = true;
}
// ... other members here
}
When obtaining an instance of this object via DataContractSerializer
you will see that the field _wasConstructorCalled
is false
.
So, how does WCF do this? Is this a technique that others can use too, or is it hidden away from us?
FormatterServices.GetUninitializedObject()
will create an instance without calling a constructor. I found this class by using Reflector and digging through some of the core .Net serialization classes.
I tested it using the sample code below and it looks like it works great:
using System;
using System.Reflection;
using System.Runtime.Serialization;
namespace NoConstructorThingy
{
class Program
{
static void Main()
{
// does not call ctor
var myClass = (MyClass)FormatterServices.GetUninitializedObject(typeof(MyClass));
Console.WriteLine(myClass.One); // writes "0", constructor not called
Console.WriteLine(myClass.Two); // writes "0", field initializer not called
}
}
public class MyClass
{
public MyClass()
{
Console.WriteLine("MyClass ctor called.");
One = 1;
}
public int One { get; private set; }
public readonly int Two = 2;
}
}
http://d3j5vwomefv46c.cloudfront.net/photos/large/687556261.png