Use Custom Events from your WCF ServiceHost

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):

//////////////////////////////////////////////////////////////////////////////////////
[ServiceContract]
public interface IMyService
{
    [OperationContract]
    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, "");
SvcHost.Open();

// 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