WCF Service Client Lifetime

Question

I have a WPF appliction that uses WCF services to make calls to the server.

I use this property in my code to access the service

private static IProjectWcfService ProjectService
{
    get
    {
        _projectServiceFactory = new ProjectWcfServiceFactory();
        return _projectServiceFactory.Create();
    }
}

The Create on the factory looks like this

    public IProjectWcfService Create()
    {
        _serviceClient = new ProjectWcfServiceClient();

        //ToDo: Need some way of saving username and password 
        _serviceClient.ClientCredentials.UserName.UserName = "MyUsername";
        _serviceClient.ClientCredentials.UserName.Password = "MyPassword";

        return _serviceClient;
    }

To access the service methods I use somethingn like the following.

ProjectService.Save(dto);

Is this a good approach for what I am trying to do? I am getting an errorthat I can't track down that I think may be realted to having too many service client connections open (is this possible?) notice I never close the service client or reuse it.

What would the best practice for WCF service client's be for WPF calling?

Thanks in advance...

Answer 1

You're on the right track, I'd say ;-)

Basically, creating the WCF client proxy is a two-step process:

• create the channel factory
• from the channel factory, create the actual channel

Step #1 is quite "expensive" in terms of time and effort needed - so it's definitely a good idea to do that once and then cache the instance of ProjectWcfServiceFactory somewhere in your code.

Step #2 is actually pretty lightweight, and since a channel between a client and a service can fall into a "faulted state" when an exception happens on the server (and then needs to be re-created from scratch), caching the actual channel per se is less desirable.

So the commonly accepted best practice would be:

• create the ChannelFactory<T> (in your case: ProjectWcfServiceFactory) once and cache it for as long as possible; do that heavy lifting only once

• create the actual Channel (here: IProjectWcfService) as needed, before every call. That way, you don't have to worry about checking its state and recreating it as needed

UPDATE: "what about closing the channel?" asks Burt ;-) Good point!!

The acccepted best practice for this is to wrap your service call in a try....catch....finally block. The tricky part is: upon disposing of the channel, things can do wrong, too, so you could get an exception - that's why wrapping it in a using(....) block isn't sufficient.

So basically you have:

IProjectWcfService client = ChannelFactory.CreateChannel();
try
{
   client.MakeYourCall();
}
catch(CommunicationException ce)
{
    // do any exception handling of your own
}
finally
{
    ICommunicationObject comObj = ((ICommunicationObject)client);

    if(comObj.State == CommunicationState.Faulted)
    {
       comObj.Abort();
    }   
    else
    {
       comObj.Close();
    }
}

And of course, you could definitely nicely wrap this into a method or an extension method or something in order not to have to type this out every time you make a service call.

UPDATE:

The book I always recommend to get up and running in WCF quickly is Learning WCF by Michele Leroux Bustamante. She covers all the necessary topics, and in a very understandable and approachable way. This will teach you everything - basics, intermediate topics, security, transaction control and so forth - that you need to know to write high quality, useful WCF services.

Learning WCF http://ecx.images-amazon.com/images/I/41wYa%2BNiPML._BO2,204,203,200_PIsitb-sticker-arrow-click,TopRight,35,-76_AA240_SH20_OU01_.jpg

The more advanced topics and more in-depth look at WCF will be covered by Programming WCF Services by Juval Lowy. He really dives into all technical details and topics and presents "the bible" for WCF programming.