IObjectReference.GetRealObject Method (StreamingContext)


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

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

Function GetRealObject (
	context As StreamingContext
) As Object


Type: System.Runtime.Serialization.StreamingContext

The StreamingContext from which the current object is deserialized.

Return Value

Type: System.Object

Returns the actual object that is put into the graph.

Exception Condition

The caller does not have the required permission. The call will not work on a medium trusted server.

This method is useful in a remoting situation where you serialize a proxy-creator object, not an actual object. When the proxy-creator object is deserialized, deserialization calls its GetRealObject method. At this point, the proxy-creator object creates a new instance of the proxy object that refers back to the original actual object, perhaps on a remote computer. Finally, the proxy-creator object is discarded and reclaimed later by garbage collection.

For example, consider how Type objects are serialized. Instead of transmitting the data from the Type object, the system transmits a holder object with the name of the type object and information on the assembly where it is found in an object implementing IObjectReference. When both the type name and assembly name are available, the deserialization infrastructure calls GetRealObject on the holder object that has been transmitted. This holder returns the Type object that is inserted into the graph.

This method is protected by a SecurityAction.LinkDemand for the SecurityPermission with the SecurityPermissionFlag.SerializationFormatter specified.

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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