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Posted 26 Jan 2011

Use Custom Events from your WCF ServiceHost

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When you need to communicate with the app that contains your ServiceHost object, use custom events
While working on an article for CodeProject, I happened on a requirement to create a WCF service using NamedPipe binding. The client application (a Windows Service) would be sending periodic messages, and if the sever (a SysTray application) was listening, it would insert those messages into a ListBox (I have no need to write the messages to disk anywhere - I just want to show them in a ListBox). This tip involves allowing the ServiceHost instance communicating to the host application that it had received a message from the client by way of a custom event.

First, you need your custom event:

public class MyHostEventArgs
    public string   Message { get; set; }
    public DateTime Date    { get; set; }
    public MyHostEventArgs(string msg, DateTime datetime)
        this.Message = msg;
        this.Date    = datetime;

public delegate void MyHostEventHandler(object sender, MyHostEventArgs e);

Next, you need to define your service (and this is where most of the tip lies):

public interface IMyService
    void SendStatusMessageEx(string msg, DateTime datetime);

[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single, IncludeExceptionDetailInFaults=true)]
public class MyService : IMyService
    public event MyHostEventHandler MyHostEvent = delegate{};

    public MyService()

    public void SendStatusMessageEx(string msg, DateTime datetime)
        MyHostEvent(this, new MyHostEventArgs(msg, datetime));

Notice the ServiceBehavior attribute. When you set the InstanceContextMode to Single, you can then do the following in your application:

// create and open an instance of the host in our form object
Uri                 BaseAddress      = new Uri("net.pipe://localhost/MyService");
NetNamedPipeBinding NamedPipeBinding = new NetNamedPipeBinding(NetNamedPipeSecurityMode.None);
MyService           svc              = new MyService();
SvcHost                              = new ServiceHost(svc, BaseAddress);
SvcHost.AddServiceEndpoint(typeof(IMyService), NamedPipeBinding, "");

// now we can add an event handler
(SvcHost.SingletonInstance as MyService).MyHostEvent += new MyHostEventHandler(Form1_MyHostEvent);

An alternative to doing this is to set up delegates inside the ServiceHost object, but that requires a tighter coupling between the object that contains the ServiceHost object, and the ServiceHost object itself.

Note: Special thanks goes out to Nish for showing me the appropriate ServiceBehavior attribute


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

John Simmons / outlaw programmer
Software Developer (Senior) Paddedwall Software
United States United States
I've been paid as a programmer since 1982 with experience in Pascal, and C++ (both self-taught), and began writing Windows programs in 1991 using Visual C++ and MFC. In the 2nd half of 2007, I started writing C# Windows Forms and ASP.Net applications, and have since done WPF, Silverlight, WCF, web services, and Windows services.

My weakest point is that my moments of clarity are too brief to hold a meaningful conversation that requires more than 30 seconds to complete. Thankfully, grunts of agreement are all that is required to conduct most discussions without committing to any particular belief system.

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Comments and Discussions

QuestionHow to handle wcf custom event under windows form in client project Pin
farzadniknam6477-Nov-14 4:20
professionalfarzadniknam6477-Nov-14 4:20 
QuestionHow would this work when the ServiceHost is running in a separate thread? Pin
johnbMA21-Apr-13 13:25
memberjohnbMA21-Apr-13 13:25 
GeneralThank you, Thank You, THANK YOU! Pin
percidae14-Feb-11 3:55
memberpercidae14-Feb-11 3:55 

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