Wait for an WCF Service to complete

Question

Hi friends

I am struggling with my wcf service in silverlight4 application.How can I wait for an async WCF service to complete?please give me a solution .I am waiting for your reply.My code is given below

ServiceReference1.DragAndDropClient client = new SilApp.ServiceReference1.DragAndDropClient();
client.GetSublayersCompleted += new EventHandler<SilApp.ServiceReference1.GetSublayersCompletedEventArgs>GetSublayer);
client.GetSublayersAsync(1);


Thanks
Sujina