Question

In our WCF project, we are using singleton pattern to obtain client proxy.

Basically because-

1. Any enhancements required later, on the client object adding
   Binding or Endpoint, would require minimal changes.
2. We do not call multiple service, at the same time.

To make sure that connection is closed properly after each service call, We are planning to implement IDisposable in singleton as below –

public class ClientSingleton : IDisposable
{
    static Service1Client client;
    private ClientSingleton()
    {
        client = new Service1Client();
    }
    public Service1Client getInstance()
    {
        if (client != null)
            return client;
        else
        {
            client = new Service1Client();
            return client;
        }
    }
    public void Dispose()
    {
        client.Close();
    }
}

Does this violates Singleton Design-Pattern principles? Any advice to improve this would be helpful.

edit:

Consider using block to dispose the client object as below –

using (Service1Client client = new Service1Client())
{
    client.Operation1();
}

That means WCF proxies implement IDisposable interface. So I don’t see any harm in implementing this interface here.

Thanks!

Answer 1

I have been using an extension method in my project that takes care of closing the service connection properly. (I stole the extension method from some blog and I forgot that blog link)

public static void CloseConnection(this ICommunicationObject client)
{
  if (client.State != CommunicationState.Opened)
  {
    return;
  }

  try
  {
    client.Close();
  }
  catch (CommunicationException)
  {
    client.Abort();
    throw;
  }
  catch (TimeoutException)
  {
    client.Abort();
    throw;
  }
  catch (Exception)
  {
    client.Abort();
    throw;
  }
}

Unlike your approach (which is specific to a particular proxy) this can be used on any proxy to close the connection safely.

Example usage

Service1Client client = null

try
{
  client = new Service1Client();
}
finally
{
  if(client != null)
     client.CloseConnection();
}