using System;

namespace SLAsyncTest.Helper
{
   public interface IResult
   {
       void Execute();
       event EventHandler Completed;
   }
}

using System;
using System.Collections.Generic;

namespace SLAsyncTest.Helper
{
   public class ResultEnumerator
   {
       private readonly IEnumerator<IResult> _enumerator;

       public ResultEnumerator(IEnumerable<IResult> children)
       {
           _enumerator = children.GetEnumerator();
       }

       public void Enumerate()
       {
           childCompleted(null, EventArgs.Empty);
       }

       private void childCompleted(object sender, EventArgs args)
       {
           var previous = sender as IResult;

           if (previous != null)
               previous.Completed -= childCompleted;

           if (!_enumerator.MoveNext())
               return;

           var next = _enumerator.Current;
           next.Completed += childCompleted;
           next.Execute();
       }
   }
}

using System.ServiceModel;
using System.ServiceModel.Activation;
using System.Threading;

namespace SLAsyncTest.Web
{
   [ServiceContract(Namespace = "")]
   [AspNetCompatibilityRequirements(RequirementsMode
       = AspNetCompatibilityRequirementsMode.Allowed)]
   public class TestService
   {
       [OperationContract]
       public int GetNumber(int number)
       {
           Thread.Sleep(2000);//Simulating a log running operation
           return number * 2;
       }
   }
}

using System;
using SLAsyncTest.Helper;

namespace SLAsyncTest.Model
{
   public class GetNumber : IResult
   {
       public int Result { set; get; }
       public bool HasError { set; get; }

       private int _num;
       public GetNumber(int num)
       {
           _num = num;
       }

       #region IResult Members
       public void Execute()
       {
           var srv = new TestServiceReference.TestServiceClient();
           srv.GetNumberCompleted += (sender, e) =>
           {
               if (e.Error == null)
                   Result = e.Result;
               else
                   HasError = true;

               Completed(this, EventArgs.Empty); //run the next IResult
           };
           srv.GetNumberAsync(_num);
       }

       public event EventHandler Completed;
       #endregion
   }
}

       private void doFetch(object obj)
       {
           new ResultEnumerator(executeAsyncOps()).Enumerate();
       }

       private IEnumerable<IResult> executeAsyncOps()
       {
           FinalResult = 0;
           IsBusy = true; //Show BusyIndicator

           //Sequential Async Operations
           var asyncOp1 = new GetNumber(10);
           yield return asyncOp1;

           //using the result of the previous step
           if(asyncOp1.HasError)
           {
               IsBusy = false; //Hide BusyIndicator
               yield break;
           }

           var asyncOp2 = new GetNumber(asyncOp1.Result);
           yield return asyncOp2;

           FinalResult = asyncOp2.Result; //Bind it to the UI

           IsBusy = false; //Hide BusyIndicator
       }