Now both methods get called before the constructor gets called
No, the order is:
- OnDeserializingMethod
- .ctor
- OnDeserializedMethod
And how can a (non-static) method be called before any constructor has been executed?
Because it cheats and lies; it doesn't create the object with the constructor; no - really. It uses FormatterServices.GetUninitializedObject to allocate vanilla empty space. And then if there is a custom deserialization constructor it invokes the constructor over the top of that object. Nasty. Like this, basically:
var obj = FormatterServices.GetUninitializedObject(typeof(MyClass));
var ctor = obj.GetType().GetConstructor(
BindingFlags.Instance | BindingFlags.Public| BindingFlags.NonPublic,
null,
new[] { typeof(SerializationInfo), typeof(StreamingContext) },
null);
ctor.Invoke(obj, new object[2]);
IMO they probably should have made this a second method on the ISerializable interface, but for whatever reason: they didn't. A shame really: that would have made it more honest, and avoided people needing to remember to implement the custom constructor.
Example output:
.ctor: MyClass
> serializing
OnSerializingMethod: MyClass
GetObjectData: MyClass
OnSerializedMethod: MyClass
< serializing
> deserializing
OnDeserializingMethod: MyClass
.ctor: MyClass
OnDeserializedMethod: MyClass
< deserializing
Example code:
using System;
using System.IO;
using System.Runtime.CompilerServices;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;
[Serializable]
class MyClass : ISerializable
{
public MyClass() { Trace(); }
protected MyClass(SerializationInfo info, StreamingContext context) { Trace(); }
public void GetObjectData(SerializationInfo info, StreamingContext context) { Trace(); }
void Trace([CallerMemberName] string caller = null)
{
System.Console.WriteLine("{0}: {1}", caller, GetType().Name);
}
[OnDeserializing()]
internal void OnDeserializingMethod(StreamingContext context) { Trace(); }
[OnDeserialized()]
internal void OnDeserializedMethod(StreamingContext context) { Trace(); }
[OnSerializing()]
internal void OnSerializingMethod(StreamingContext context) { Trace(); }
[OnSerialized()]
internal void OnSerializedMethod(StreamingContext context) { Trace(); }
static void Main()
{
using (var ms = new MemoryStream())
{
var orig = new MyClass();
var ser = new BinaryFormatter();
System.Console.WriteLine("> serializing");
ser.Serialize(ms, orig);
System.Console.WriteLine("< serializing");
ms.Position = 0;
System.Console.WriteLine("> deserializing");
ser.Deserialize(ms);
System.Console.WriteLine("< deserializing");
}
}
}
