Chapter 125: Binary Serialization

Section 125.1: Controlling serialization behavior with attributes

If you use the [NonSerialized] attribute, then that member will always have its default value after deserialization (ex. 0 for an int, null for string, false for a bool, etc.), regardless of any initialization done in the object itself (constructors, declarations, etc.). To compensate, the attributes [OnDeserializing] (called just BEFORE deserializing) and [OnDeserialized] (called just AFTER deserializing) together with their counterparts,

[OnSerializing] and [OnSerialized] are provided.

Assume we want to add a "Rating" to our Vector and we want to make sure the value always starts at 1. The way it is written below, it will be 0 after being deserialized:

[Serializable] public class Vector

{

public int X; public int Y; public int Z;

[NonSerialized]

public decimal Rating = 1M;

public Vector()

{

Rating = 1M;

}

public Vector(decimal initialRating)

{

Rating = initialRating;

}

}

To fix this problem, we can simply add the following method inside of the class to set it to 1:

[OnDeserializing]

void OnDeserializing(StreamingContext context)

{

Rating = 1M;

}

Or, if we want to set it to a calculated value, we can wait for it to be finished deserializing and then set it:

[OnDeserialized]

void OnDeserialized(StreamingContext context)

{

Rating = 1 + ((X+Y+Z)/3);

}

Similarly, we can control how things are written out by using [OnSerializing] and [OnSerialized].

Section 125.2: Serialization Binder

The binder gives you an opportunity to inspect what types are being loaded in your application domain

Create a class inherited from SerializationBinder

class MyBinder : SerializationBinder

{

public override Type BindToType(string assemblyName, string typeName)

{

if (typeName.Equals("BinarySerializationExample.Item")) return typeof(Item);

return null;

}

}

Now we can check what types are loading and on this basis to decide what we really want to receive

For using a binder, you must add it to the BinaryFormatter.

object DeserializeData(byte[] bytes)

{

var binaryFormatter = new BinaryFormatter(); binaryFormatter.Binder = new MyBinder();

using (var memoryStream = new MemoryStream(bytes)) return binaryFormatter.Deserialize(memoryStream);

}

The complete solution

using System; using System.IO;

using System.Runtime.Serialization;

using System.Runtime.Serialization.Formatters.Binary;

namespace BinarySerializationExample

{

class MyBinder : SerializationBinder

{

public override Type BindToType(string assemblyName, string typeName)

{

if (typeName.Equals("BinarySerializationExample.Item")) return typeof(Item);

return null;

}

}

[Serializable] public class Item

{

private string _name;

public string Name

{

get { return _name; } set { _name = value; }

}

}

class Program

{

static void Main(string[] args)

{

var item = new Item

{

Name = "Orange"

};

var bytes = SerializeData(item);

var deserializedData = (Item)DeserializeData(bytes);

}

private static byte[] SerializeData(object obj)

{

var binaryFormatter = new BinaryFormatter(); using (var memoryStream = new MemoryStream())

{

binaryFormatter.Serialize(memoryStream, obj); return memoryStream.ToArray();

}

}

private static object DeserializeData(byte[] bytes)

{

var binaryFormatter = new BinaryFormatter

{

Binder = new MyBinder()

};

using (var memoryStream = new MemoryStream(bytes)) return binaryFormatter.Deserialize(memoryStream);

}

}

}

Section 125.3: Some gotchas in backward compatibility

This small example shows how you can lose backward compatibility in your programs if you do not take care in advance about this. And ways to get more control of serialization process

At first, we will write an example of the first version of the program:

Version 1

[Serializable] class Data

{

[OptionalField] private int _version;

public int Version

{

get { return _version; } set { _version = value; }

}

}

And now, let us assume that in the second version of the program added a new class. And we need to store it in an array.

Now code will look like this: