OperationContext.GetCallbackChannel OperationContext.GetCallbackChannel OperationContext.GetCallbackChannel OperationContext.GetCallbackChannel Method

Definition

Gets a channel to the client instance that called the current operation.

public:
generic <typename T>
 T GetCallbackChannel();
public T GetCallbackChannel<T> ();
member this.GetCallbackChannel : unit -> 'T
Public Function GetCallbackChannel(Of T) () As T

Type Parameters

T

The type of channel used to call back to the client.

Returns

T T T T

A channel to the client instance that called the operation of the type specified in the CallbackContract property.

Examples

The following code example uses the Current property and GetCallbackChannel method to create a channel back to the caller from within a operation. All operations in this example are one-way operations, enabling the service and the client to communicate in both directions independently. In this case, the example client application expects only one return call before it exits, but another client, for example a Windows Forms client, can receive any number of calls from the service.

using System;
using System.Collections.Generic;
using System.ServiceModel;
using System.Threading;

namespace Microsoft.WCF.Documentation
{
  [ServiceContract(
    Name = "SampleDuplexHello",
    Namespace = "http://microsoft.wcf.documentation",
    CallbackContract = typeof(IHelloCallbackContract),
    SessionMode = SessionMode.Required
  )]
  public interface IDuplexHello
  {
    [OperationContract(IsOneWay = true)]
    void Hello(string greeting);
  }

  public interface IHelloCallbackContract
  {
    [OperationContract(IsOneWay = true)]
    void Reply(string responseToGreeting);
  }

  public class DuplexHello : IDuplexHello
  {
    public DuplexHello()
    {
      Console.WriteLine("Service object created: " + this.GetHashCode().ToString());
    }

    ~DuplexHello()
    {
      Console.WriteLine("Service object destroyed: " + this.GetHashCode().ToString());
    }

    public void Hello(string greeting)
    {
      Console.WriteLine("Caller sent: " + greeting);
      Console.WriteLine("Session ID: " + OperationContext.Current.SessionId);
      Console.WriteLine("Waiting two seconds before returning call.");
      // Put a slight delay to demonstrate asynchronous behavior on client.
      Thread.Sleep(2000);
      IHelloCallbackContract callerProxy
        = OperationContext.Current.GetCallbackChannel<IHelloCallbackContract>();
      string response = "Service object " + this.GetHashCode().ToString() + " received: " + greeting;
      Console.WriteLine("Sending back: " + response);
      callerProxy.Reply(response);
    }
  }
}


Imports System
Imports System.Collections.Generic
Imports System.ServiceModel
Imports System.Threading

Namespace Microsoft.WCF.Documentation
    <ServiceContract(Name:="SampleDuplexHello", Namespace:="http://microsoft.wcf.documentation", _
                     CallbackContract:=GetType(IHelloCallbackContract), SessionMode:=SessionMode.Required)> _
  Public Interface IDuplexHello
        <OperationContract(IsOneWay:=True)> _
        Sub Hello(ByVal greeting As String)
    End Interface

  Public Interface IHelloCallbackContract
	<OperationContract(IsOneWay := True)> _
	Sub Reply(ByVal responseToGreeting As String)
  End Interface

  Public Class DuplexHello
	  Implements IDuplexHello
	Public Sub New()
	  Console.WriteLine("Service object created: " & Me.GetHashCode().ToString())
	End Sub

	Protected Overrides Sub Finalize()
	  Console.WriteLine("Service object destroyed: " & Me.GetHashCode().ToString())
	End Sub

	Public Sub Hello(ByVal greeting As String) Implements IDuplexHello.Hello
	  Console.WriteLine("Caller sent: " & greeting)
	  Console.WriteLine("Session ID: " & OperationContext.Current.SessionId)
	  Console.WriteLine("Waiting two seconds before returning call.")
	  ' Put a slight delay to demonstrate asynchronous behavior on client.
	  Thread.Sleep(2000)
            Dim callerProxy = OperationContext.Current.GetCallbackChannel(Of IHelloCallbackContract)()
            Dim response = "Service object " & Me.GetHashCode().ToString() & " received: " & greeting
	  Console.WriteLine("Sending back: " & response)
	  callerProxy.Reply(response)
	End Sub
  End Class
End Namespace

The following client implements the SampleDuplexHelloCallback to receive the callback message. The imported callback contract is not the same name as the one in the service, due to the use of the Name property in the preceding example. Note that the client makes no assumptions about whether or when it might receive a callback; the server callback is entirely independent of the client's outbound call.

Note

For an example that uses the OperationContext class in a client scenario, see OperationContextScope.

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

namespace Microsoft.WCF.Documentation
{
  public class Client : SampleDuplexHelloCallback
  {
    AutoResetEvent waitHandle;

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

    public void Run()
    {
      // Picks up configuration from the config file.
      SampleDuplexHelloClient wcfClient 
        = new SampleDuplexHelloClient(new InstanceContext(this));
      try
      {
        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);
        wcfClient.Hello(greeting);
        Console.WriteLine("Execution passes service call and moves to the WaitHandle.");
        this.waitHandle.WaitOne();
        Console.ForegroundColor = ConsoleColor.Blue;
        Console.WriteLine("Set was called.");
        Console.Write("Press ");
        Console.ForegroundColor = ConsoleColor.Red;
        Console.Write("ENTER");
        Console.ForegroundColor = ConsoleColor.Blue;
        Console.Write(" to exit...");
        Console.ReadLine();
        wcfClient.Close();
      }
      catch (TimeoutException timeProblem)
      {
        Console.WriteLine("The service operation timed out. " + timeProblem.Message);
        Console.ReadLine();
        wcfClient.Abort();
      }
      catch (CommunicationException commProblem)
      {
        Console.WriteLine("There was a communication problem. " + commProblem.Message);
        Console.ReadLine();
        wcfClient.Abort();
      }
    }

    public static void Main()
    {
      Client client = new Client();
      client.Run();
    }

    public void Reply(string response)
    {
      Console.WriteLine("Received output.");
      Console.WriteLine("\r\n\t" + response);
      this.waitHandle.Set();
    }
  }
}

Imports Microsoft.VisualBasic
Imports System
Imports System.ServiceModel
Imports System.ServiceModel.Channels
Imports System.Threading

Namespace Microsoft.WCF.Documentation
  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 config file.
	  Dim wcfClient As New SampleDuplexHelloClient(New InstanceContext(Me))
	  Try
		Console.ForegroundColor = ConsoleColor.White
		Console.WriteLine("Enter a greeting to send and press ENTER: ")
		Console.Write(">>> ")
		Console.ForegroundColor = ConsoleColor.Green
                Dim greeting = Console.ReadLine()
		Console.ForegroundColor = ConsoleColor.White
		Console.WriteLine("Called service with: " & Constants.vbCrLf & Constants.vbTab & greeting)
		wcfClient.Hello(greeting)
		Console.WriteLine("Execution passes service call and moves to the WaitHandle.")
		Me.waitHandle.WaitOne()
		Console.ForegroundColor = ConsoleColor.Blue
		Console.WriteLine("Set was called.")
		Console.Write("Press ")
		Console.ForegroundColor = ConsoleColor.Red
		Console.Write("ENTER")
		Console.ForegroundColor = ConsoleColor.Blue
		Console.Write(" to exit...")
		Console.ReadLine()
		wcfClient.Close()
	  Catch timeProblem As TimeoutException
		Console.WriteLine("The service operation timed out. " & timeProblem.Message)
		Console.ReadLine()
		wcfClient.Abort()
	  Catch commProblem As CommunicationException
		Console.WriteLine("There was a communication problem. " & commProblem.Message)
		Console.ReadLine()
		wcfClient.Abort()
	  End Try
	End Sub

	Public Shared Sub Main()
	  Dim client As New Client()
	  client.Run()
	End Sub

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

Remarks

Call the GetCallbackChannel property to obtain a channel that you can use to call operations on the client instance that called the service.

Applies to