Microsoft Visio 2010 : Custom Serialization

Listing 1. Providing Custom Serialization

Imports System.Runtime.Serialization
Imports System.Security.Permissions

<Serializable()>
Public Class Person
    Implements ISerializable

    Public Overridable Property FirstName As String
    Public Overridable Property LastName As String
    Public Overridable Property Age As Integer

    <SecurityPermission(SecurityAction.Demand,
                        SerializationFormatter:=True)>
    Protected Sub GetObjectData(ByVal info As System.Runtime.Serialization.
                                              SerializationInfo,
                                ByVal context As System.Runtime.Serialization.
                                              StreamingContext) _
                              Implements System.Runtime.Serialization.ISerializable.
                                              GetObjectData

        info.AddValue("First name", Me.FirstName)
        info.AddValue("Last name", Me.LastName)
        info.AddValue("Age", Me.Age)
    End Sub

    'At deserialization time
    Protected Sub New(ByVal info As SerializationInfo,
                      ByVal context As StreamingContext)
        MyBase.New()
        Me.FirstName = info.GetString("First name")
        Me.LastName = info.GetString("Last name")
        Me.Age = info.GetInt32("Age")
    End Sub
End Class

					  

The GetObjectData method is basically invoked when you pass an object to the Serialize method of a formatter and require an info argument of type SerializationInfo. This class stores all information needed for serialization. It exposes an AddValue method that stores data and a value utilized for recognizing data. Notice that the information is retrieved by the special constructor implementation that is invoked at deserialization time via GetXXX methods where XXX corresponds to .NET types such as Int32, Boolean, Short, and so on. Also notice how GetObjectData is decorated with the SecurityPermission attribute demanding for permissions about the serialization formatter. This is necessary because the permission is allowed only to full-trusted code, thus intranet and Internet zones are not allowed. Both GetObjectData and the constructor are Protected so that derived classes can still take advantage of them but are prevented from being public. If you are sure that your class will not be inherited, GetObjectData can also be Private.

Implementing ISerializable is not the only way for controlling serialization. You can control serialization events, too.

Serialization Events

The serialization process raises four events, which are summarized in Table 1.

Serialization events are handled differently than classic events. There is an attribute for each event that you can handle as follows:

'Invoke this method before
'serialization begins
<OnSerializing()>
Private Sub FirstMethod()

End Sub

'Invoke this method after
'serialization completes
<OnSerialized()>
Private Sub SecondMethod()

End Sub

'Invoke this method before
'deserialization begins
<OnDeserializing()>
Private Sub ThirdMethod()

End Sub

'Invoke this method after
'deserialization completes
<OnDeserialized()>
Private Sub FourthMethod()

End Sub

The runtime takes care of invoking the specified method according to the moment represented by each attribute. In this way you can provide additional actions based on serialization events.