Free-ebooks-library - Bahar Ali Khan

[OnSerializing] and [OnSerialized]
The binary engine also supports the [OnSerializing] and [OnSerialized] attributes.
These flag a method for execution before or after serialization. To see how they can
be useful, we’ll define a Team class that contains a generic List of players:
[Serializable] public sealed class Team
{
public string Name;
public List Players = new List();
}
This class serializes and deserializes correctly with the binary formatter but not the
SOAP formatter. This is because of an obscure limitation: the SOAP formatter refuses
to serialize generic types! An easy solution is to convert Players to an array just
prior to serialization, then convert it back to a generic List upon deserialization. To
make this work, we can add another field for storing the array, mark the original
Players field as [NonSerialized], and then write the conversion code in as follows:
[Serializable] public sealed class Team
{
public string Name;
Person[] _playersToSerialize;
[NonSerialized] public List Players = new List();
[OnSerializing]
void OnSerializing (StreamingContext context)
{
_playersToSerialize = Players.ToArray();
}
[OnSerialized]
void OnSerialized (StreamingContext context)
{
_playersToSerialize = null; // Allow it to be freed from memory
}
[OnDeserialized]
void OnDeserialized (StreamingContext context)
{
Players = new List (_playersToSerialize);
}
}
[OptionalField] and Versioning
By default, adding a field breaks compatibility with data that’s already serialized,
unless you attach the [OptionalField] attribute to the new field.
To illustrate, suppose we start with a Person class that has just one field. Let’s call
it Version 1:
632 | Chapter 16: Serialization