title: How to call wcf service Asynchronously
body: <p>if wcf service is design the below way then please guide me how call <code>Add()</code> function <code>Asynchronously</code> from client side. thanks</p>
  
  <pre><code>[ServiceContract]
  public interface IAddTwoNumbers
  {
      // If the asynchronous method pair
      // appears on the client channel, the client can call 
      // them asynchronously to prevent blocking.
      [OperationContract (AsyncPattern=true)]
      IAsyncResult BeginAdd(int a, int b, AsyncCallback cb, AsyncState s);
  
      [OperationContract]
      int EndAdd(IAsyncResult r);
  
      // This is a synchronous version of the BeginAdd/EndAdd pair.
      // It appears in the client channel code by default. 
      [OperationContract]
      int Add(int a, int b);
     }
  </code></pre>