IObjectReference Interface


Indicates that the current interface implementer is a reference to another object.

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

Public Interface IObjectReference


Returns the real object that should be deserialized, rather than the object that the serialized stream specifies.

Notes to Implementers:

Implement this interface on objects that are references to a different object, which cannot be resolved until the current object is completely restored. During the fixup stage, any object implementing IObjectReference is queried for its real object and that object is inserted into the graph. Fixup refers to the process of finalizing references not already completed during the object deserialization process.

Imports System
Imports System.Web
Imports System.IO
Imports System.Collections
Imports System.Runtime.Serialization.Formatters.Binary
Imports System.Runtime.Serialization
Imports System.Security.Permissions

' There should be only one instance of this type per AppDomain.
<Serializable()> _
<PermissionSet(SecurityAction.Demand, Name:="FullTrust")> _
Public NotInheritable Class Singleton
   Implements ISerializable

   ' This is the one instance of this type.
   Private Shared ReadOnly theOneObject As New Singleton

   ' Here are the instance fields.
   Private someString As String
   private someNumber As Int32

   ' Private constructor allowing this type to construct the Singleton.
   Private Sub New()
      ' Do whatever is necessary to initialize the Singleton.
      someString = "This is a string field"
      someNumber = 123
   End Sub

   ' A method returning a reference to the Singleton.
   Public Shared Function GetSingleton() As Singleton
      Return theOneObject
   End Function

   ' A method called when serializing a Singleton.
   <SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags:=SecurityPermissionFlag.SerializationFormatter)> _
   Private Sub GetObjectData(ByVal info As SerializationInfo, _
      ByVal context As StreamingContext) _
      Implements ISerializable.GetObjectData

      ' Instead of serializing this object, we will  
      ' serialize a SingletonSerializationHelp instead.
      ' No other values need to be added.
   End Sub

   ' Note: ISerializable's special constructor is not necessary 
   ' because it is never called.
End Class

<Serializable()> _
<PermissionSet(SecurityAction.Demand, Name:="FullTrust")> _
Friend NotInheritable Class SingletonSerializationHelper
   Implements IObjectReference
   ' This object has no fields (although it could).

   ' GetRealObject is called after this object is deserialized.
   <SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags:=SecurityPermissionFlag.SerializationFormatter)> _
   Public Function GetRealObject(ByVal context As StreamingContext) As Object Implements IObjectReference.GetRealObject
      ' When deserialiing this object, return a reference to 
      ' the Singleton object instead.
      Return Singleton.GetSingleton()
   End Function
End Class

Class App
   <STAThread()> Shared Sub Main()
      Dim fs As New FileStream("DataFile.dat", FileMode.Create)

         ' Construct a BinaryFormatter and use it 
         ' to serialize the data to the stream.
         Dim formatter As New BinaryFormatter

         ' Create an array with multiple elements refering to 
         ' the one Singleton object.
         Dim a1() As Singleton = {Singleton.GetSingleton(), Singleton.GetSingleton()}

         ' This displays "True".
         Console.WriteLine("Do both array elements refer to the same object? " & _
            Object.ReferenceEquals(a1(0), a1(1)))

         ' Serialize the array elements.
         formatter.Serialize(fs, a1)

         ' Deserialize the array elements.
         fs.Position = 0
         Dim a2() As Singleton = DirectCast(formatter.Deserialize(fs), Singleton())

         ' This displays "True".
         Console.WriteLine("Do both array elements refer to the same object? " & _
            Object.ReferenceEquals(a2(0), a2(1)))

         ' This displays "True".
         Console.WriteLine("Do all array elements refer to the same object? " & _
            Object.ReferenceEquals(a1(0), a2(0)))
      Catch e As SerializationException
         Console.WriteLine("Failed to serialize. Reason: " & e.Message)
      End Try
   End Sub
End Class

.NET Framework
Available since 1.1
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