Exception.SerializeObjectState Event

.NET Framework (current version)

Occurs when an exception is serialized to create an exception state object that contains serialized data about the exception.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

C++

Protected Event SerializeObjectState As EventHandler(Of SafeSerializationEventArgs)

Remarks

The exception state object implements the ISafeSerializationData interface.

When the SerializeObjectState event is subscribed to, the exception is deserialized and created as an empty exception. The exception's constructor is not run, and the exception state is also deserialized. The CompleteDeserialization callback method of the exception state object is then notified so that it can push deserialized data into the empty exception.

The SerializeObjectState event enables transparent exception types to serialize and deserialize exception data. Transparent code can execute commands within the bounds of the permission set it is operating within, but cannot execute, call, derive from, or contain critical code.

If the SerializeObjectState event is not subscribed to, deserialization occurs as usual using the Exception constructor.

Typically, a handler for the SerializeObjectState event is added in the exception's constructor to provide for its serialization. But because the constructor is not executed when the SerializeObjectState event handler executes, serializing a deserialized exception can throw a SerializationException exception when you try to deserialize the exception. To avoid this, you should also add the handler for the SerializeObjectState event in the ISafeSerializationData.CompleteDeserialization method. See the Examples section for an illustration.

Notes to Implementers:

If this event is subscribed to and used, all derived types that follow in the inheritance hierarchy must implement the same serialization mechanism.

Examples

The following example defines a BadDivisionException that handles the SerializeObjectState event. It also contains a state object, which is a nested structure named BadDivisionExceptionState that implements the ISafeSerializationData interface.

Imports System.IO
Imports System.Runtime.Serialization
Imports System.Runtime.Serialization.Formatters.Binary

Module Example
   Public Sub Main()
      Dim serialized As Boolean = False
      Dim formatter As New BinaryFormatter()
      Dim values() As Double = { 3, 2, 1 }
      Dim divisor As Double = 0
      For Each value In values
         Try
            Dim ex As BadDivisionException = Nothing
            If divisor = 0 Then 
               If Not serialized Then
                  ' Instantiate the exception object.
                  ex = New BadDivisionException(0)
                  ' Serialize the exception object.
                  Dim fs As New FileStream("BadDivision1.dat", 
                                           FileMode.Create)
                  formatter.Serialize(fs, ex)
                  fs.Close()
                  Console.WriteLine("Serialized the exception...")
               Else
                  ' Deserialize the exception.
                  Dim fs As New FileStream("BadDivision1.dat",
                                           FileMode.Open)
                  ex = CType(formatter.Deserialize(fs), BadDivisionException)
                  ' Reserialize the exception.
                  fs.Position = 0
                  formatter.Serialize(fs, ex)
                  fs.Close()
                  Console.WriteLine("Reserialized the exception...")                                            
               End If   
              Throw ex 
            End If 
            Console.WriteLine("{0} / {1} = {1}", value, divisor, value/divisor)
         Catch e As BadDivisionException
            Console.WriteLine("Bad divisor from a {0} exception: {1}",
                              If(serialized, "deserialized", "new"), e.Divisor)             
            serialized = True
         End Try   
      Next
   End Sub
End Module

<Serializable> Public Class BadDivisionException : Inherits Exception
   ' Maintain an internal BadDivisionException state object.
   <NonSerialized> Private state As New BadDivisionExceptionState()

   Public Sub New(divisor As Double)
      state.Divisor = divisor
      HandleSerialization()      
   End Sub

   Private Sub HandleSerialization()
      AddHandler SerializeObjectState, 
                 Sub(exception As Object, eventArgs As SafeSerializationEventArgs)
                    eventArgs.AddSerializedState(state)
                 End Sub
   End Sub

   Public ReadOnly Property Divisor As Double
      Get
         Return state.Divisor
      End Get      
   End Property

   <Serializable> Private Structure BadDivisionExceptionState 
                                    Implements ISafeSerializationData
      private badDivisor As Double

      Public Property Divisor As Double
         Get
            Return badDivisor
         End Get
         Set
            badDivisor = value
         End Set
      End Property 

      Sub CompleteDeserialization(deserialized As Object) _
            Implements ISafeSerializationData.CompleteDeserialization
         Dim ex As BadDivisionException = TryCast(deserialized, BadDivisionException)
         ex.HandleSerialization()
         ex.state = Me 
      End Sub
   End Structure
End Class
' The example displays the following output:
'       Serialized the exception...
'       Bad divisor from a new exception: 0
'       Reserialized the exception...
'       Bad divisor from a deserialized exception: 0
'       Reserialized the exception...
'       Bad divisor from a deserialized exception: 0

The BadDivisionException exception is thrown when a floating-point division by zero occurs. During the first division by zero, the example instantiates a BadDivisionException object, serializes it, and throws the exception. When subsequent divisions by zero occur, the example deserializes the previously serialized object, reserializes it, and throws the exception. To provide for object serialization, deserialization, reserialization, and deserialization, the example adds the SerializeObjectState event handler both in the BadDivisionException class constructor and in the ISafeSerializationData.CompleteDeserialization implementation.

Version Information

.NET Framework
Available since 4.0