CallbackBehaviorAttribute Class


Configures a callback service implementation in a client application.

public ref class CallbackBehaviorAttribute sealed : Attribute, System::ServiceModel::Description::IEndpointBehavior
public sealed class CallbackBehaviorAttribute : Attribute, System.ServiceModel.Description.IEndpointBehavior
type CallbackBehaviorAttribute = class
    inherit Attribute
    interface IEndpointBehavior
Public NotInheritable Class CallbackBehaviorAttribute
Inherits Attribute
Implements IEndpointBehavior


The following code example shows a CallbackBehaviorAttribute on a callback object that uses the SynchronizationContext object to determine which thread to marshal to, the ValidateMustUnderstand property to enforce message validation, and the IncludeExceptionDetailInFaults property to return exceptions as FaultException objects to the service for debugging purposes.

using System;
using System.ServiceModel;
using System.ServiceModel.Channels;
using System.Threading;

namespace Microsoft.WCF.Documentation
   IncludeExceptionDetailInFaults= true,
  public class Client : SampleDuplexHelloCallback
    AutoResetEvent waitHandle;

    public Client()
      waitHandle = new AutoResetEvent(false);

    public void Run()
      // Picks up configuration from the configuration file.
      SampleDuplexHelloClient wcfClient
        = new SampleDuplexHelloClient(new InstanceContext(this), "WSDualHttpBinding_SampleDuplexHello");
        Console.ForegroundColor = ConsoleColor.White;
        Console.WriteLine("Enter a greeting to send and press ENTER: ");
        Console.Write(">>> ");
        Console.ForegroundColor = ConsoleColor.Green;
        string greeting = Console.ReadLine();
        Console.ForegroundColor = ConsoleColor.White;
        Console.WriteLine("Called service with: \r\n\t" + greeting);
        Console.WriteLine("Execution passes service call and moves to the WaitHandle.");
        Console.ForegroundColor = ConsoleColor.Blue;
        Console.WriteLine("Set was called.");
        Console.Write("Press ");
        Console.ForegroundColor = ConsoleColor.Red;
        Console.ForegroundColor = ConsoleColor.Blue;
        Console.Write(" to exit...");
      catch (TimeoutException timeProblem)
        Console.WriteLine("The service operation timed out. " + timeProblem.Message);
      catch (CommunicationException commProblem)
        Console.WriteLine("There was a communication problem. " + commProblem.Message);
    public static void Main()
      Client client = new Client();

    public void Reply(string response)
      Console.WriteLine("Received output.");
      Console.WriteLine("\r\n\t" + response);

Imports System.ServiceModel
Imports System.ServiceModel.Channels
Imports System.Threading

Namespace Microsoft.WCF.Documentation
  <CallbackBehaviorAttribute(IncludeExceptionDetailInFaults:= True, UseSynchronizationContext:=True, ValidateMustUnderstand:=True)> _
  Public Class Client
      Implements SampleDuplexHelloCallback
    Private waitHandle As AutoResetEvent

    Public Sub New()
      waitHandle = New AutoResetEvent(False)
    End Sub

    Public Sub Run()
      ' Picks up configuration from the configuration file.
      Dim wcfClient As New SampleDuplexHelloClient(New InstanceContext(Me), "WSDualHttpBinding_SampleDuplexHello")
        Console.ForegroundColor = ConsoleColor.White
        Console.WriteLine("Enter a greeting to send and press ENTER: ")
        Console.Write(">>> ")
        Console.ForegroundColor = ConsoleColor.Green
        Dim greeting As String = Console.ReadLine()
        Console.ForegroundColor = ConsoleColor.White
        Console.WriteLine("Called service with: " & Constants.vbCrLf & Constants.vbTab & greeting)
        Console.WriteLine("Execution passes service call and moves to the WaitHandle.")
        Console.ForegroundColor = ConsoleColor.Blue
        Console.WriteLine("Set was called.")
        Console.Write("Press ")
        Console.ForegroundColor = ConsoleColor.Red
        Console.ForegroundColor = ConsoleColor.Blue
        Console.Write(" to exit...")
      Catch timeProblem As TimeoutException
        Console.WriteLine("The service operation timed out. " & timeProblem.Message)
      Catch commProblem As CommunicationException
        Console.WriteLine("There was a communication problem. " & commProblem.Message)
      End Try
    End Sub
    Public Shared Sub Main()
      Dim client As New Client()
    End Sub

    Public Sub Reply(ByVal response As String) Implements SampleDuplexHelloCallback.Reply
      Console.WriteLine("Received output.")
      Console.WriteLine(Constants.vbCrLf & Constants.vbTab & response)
    End Sub
  End Class
End Namespace


Use the CallbackBehaviorAttribute attribute to configure or extend the execution behavior of a callback contract implementation in a client application. This attribute performs the same function for the callback class as the ServiceBehaviorAttribute attribute with the exception of instancing behavior and transaction settings.

The CallbackBehaviorAttribute must be applied to the class that implements the callback contract. If applied to a non-duplex contract implementation an InvalidOperationException exception is thrown at runtime.


You can also use the OperationBehaviorAttribute attribute for the callback operation implementations. However, if OperationBehaviorAttribute is used on a callback operation, the ReleaseInstanceMode property must be None or an InvalidOperationException exception is thrown at runtime.

The following properties are available:

  • The AutomaticSessionShutdown property automatically closes the session when the channel is closed and the callback has finished processing any remaining messages.

  • The ConcurrencyMode property controls the internal threading model, enabling support for reentrant or multithreaded callback objects.

  • The IgnoreExtensionDataObject property enables the runtime to ignore extra serialization information that is not required to process the message.

  • The IncludeExceptionDetailInFaults property specifies whether unhandled exceptions in a service are returned to the service as SOAP faults for debugging purposes.

  • The MaxItemsInObjectGraph property limits on the number of items in an object graph that are serialized.

  • The TransactionIsolationLevel property specifies the transaction isolation level that the contract supports.

  • The TransactionTimeout property specifies the time period within which a transaction must complete or it aborts.

  • The UseSynchronizationContext property indicates whether to synchronize inbound method calls automatically using the current SynchronizationContext object.

  • The ValidateMustUnderstand property informs the system whether it should confirm that SOAP headers marked as MustUnderstand have, in fact, been understood.



Initializes a new instance of the CallbackBehaviorAttribute class.



Specifies whether to automatically close a session when a service closes a duplex session.


Gets or sets whether a service supports one thread, multiple threads, or reentrant calls.


Gets or sets a value that specifies whether to send unknown serialization data onto the wire.


Gets or sets a value that specifies that general unhandled execution exceptions are to be converted into a FaultException<TDetail> of type String and sent as a fault message. Set this to true only during development to troubleshoot a service.


Gets or sets the maximum number of items allowed in a serialized object.


Specifies the transaction isolation level.


Gets or sets the period within which a transaction must complete.


When implemented in a derived class, gets a unique identifier for this Attribute.

(Inherited from Attribute)

Gets or sets a value that specifies whether to use the current synchronization context to choose the thread of execution.


Gets or sets a value that specifies whether the system or the application enforces SOAP MustUnderstand header processing.



Returns a value that indicates whether this instance is equal to a specified object.

(Inherited from Attribute)

Returns the hash code for this instance.

(Inherited from Attribute)

Gets the Type of the current instance.

(Inherited from Object)

When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.

(Inherited from Attribute)

When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.

(Inherited from Attribute)

Creates a shallow copy of the current Object.

(Inherited from Object)

Returns a string that represents the current object.

(Inherited from Object)

Explicit Interface Implementations

_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Maps a set of names to a corresponding set of dispatch identifiers.

(Inherited from Attribute)
_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Retrieves the type information for an object, which can be used to get the type information for an interface.

(Inherited from Attribute)

Retrieves the number of type information interfaces that an object provides (either 0 or 1).

(Inherited from Attribute)
_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Provides access to properties and methods exposed by an object.

(Inherited from Attribute)
IEndpointBehavior.AddBindingParameters(ServiceEndpoint, BindingParameterCollection)

Configures the binding elements to support the callback behavior.

IEndpointBehavior.ApplyClientBehavior(ServiceEndpoint, ClientRuntime)

Configures the client runtime to support the callback object.

IEndpointBehavior.ApplyDispatchBehavior(ServiceEndpoint, EndpointDispatcher)

Implementation of the ApplyDispatchBehavior(ServiceEndpoint, EndpointDispatcher) method. This implementation has no effect.


Validates the endpoint description prior to building the runtime.

Applies to