Service Bus IAsyncResult

Question

I'm curently trying to make my App able to receive Asyncronously message from my Service Bus. But, Sometimes an Exception is Throw and i don't know how to make it disapear or from what it can come from.

Here's the exception:

Exception: System.NullReferenceException: Object reference not set to an instance of an     object. at GetOffers.DbConnection.processEndReceive(IAsyncResult result);

So, I know it come from my IASync method, but I'm not able to understand where it don't work properly.

My QueueClient conf:

QClient = QueueClient.CreateFromConnectionString(connectionString, queueStr,ReceiveMode.ReceiveAndDelete);

Here my both IASync Method:

    void processEndReceive(IAsyncResult result)
    {
        try
        {
            QueueClient qc = result.AsyncState as QueueClient;
            BrokeredMessage message = qc.EndReceive(result);
            ForexData data = new ForexData();

            var newtrade = new Trade(data.OfferId, message.Properties["login"].ToString(), message.Properties["amount"].ToString(), message.Properties["instr"].ToString(), message.Properties["type"].ToString(), data.CreationDate, message.Properties["mode"].ToString(), message.Properties["accountID"].ToString(), message.Properties["idTrade"].ToString());
            //Static Variable for the WHERE (sql) in ResponseListener Line 215. 
            idtradetemp = message.Properties["idTrade"].ToString();
            Console.WriteLine("Received message " + message.Label);
            if (newtrade != null)
            {
                try
                {
                    newtrades.Add(newtrade);
                }
                catch
                {
                    Console.WriteLine("Une erreur est survenue lors l'ajout du message dans la liste 'newtrades'");
                }
                Console.WriteLine("Received Delete: " + DateTime.Now);
            }
        }
        catch (Exception e)
        {
            Console.WriteLine(string.Format("Exception: {0}", e.ToString()));
            TextWriter tw = new StreamWriter("logServiceBus.txt", true);
            tw.WriteLine("Program terminated on " + DateTime.Now);
            tw.WriteLine("------------------------------------");
            tw.WriteLine(string.Format("Exception: {0}", e.ToString()));
            tw.WriteLine("------------------------------------");
            tw.Close();
        }
    }

    void processEndComplete(IAsyncResult result)
    {
        try
        {
            BrokeredMessage m = result.AsyncState as BrokeredMessage;
            m.EndComplete(result);
            Console.WriteLine("Completed message " + m.Label);
        }
        catch
        { 

        }
    }

Basicaly those method are Trigger everytime he detect a new message in the ServiceBus. The thing is, I've put a Console.WriteLine("New Message"); when a new message are detected, but, this CW are trigger 2times (or more).

So One of two things: What can cause my error ? And HOW can I make my IAsync method to just be trigger once ON THIS message.

Answer 1

Using the Begin/End pairs can be difficult to program correctly. Have you tried updating your code to use the async/await pattern? Service Bus libraries for the released service as well as for Service Bus 1.1 on server also support a Task based API. See http://www.windows-azure.net/task-based-apis-for-service-bus/ for details (I'm the author of that post). You can then use ReceiveAsync. You may also want to look at the OnMessage API which will also work. (docs are here: http://msdn.microsoft.com/en-us/library/microsoft.servicebus.messaging.queueclient.onmessage.aspx)