Question

I’m a beginner at using ActiveMQ with C#. I’ve created a simple windows form with one button and one label. When I click on the button, i send a message to the queue and the label is initialized with the message I just sent. Of course, I could initialize my label directly but I want my form to rather consume the message from the queue in order to update my label.

The problem is I don’t manage to handle the message in the same form to update my label. My consumer code is not called at all and yet, its initialized in the Load event of my form.
Here’s the code

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);
        InitializeHandlerAMQ();
    }

    private void InitializeHandlerAMQ()
    {
        Tchat tchat = null;
        IDestination dest = _session.GetQueue(QUEUE_DESTINATION);
        using(IMessageConsumer consumer = _session.CreateConsumer(dest))
        {
            IMessage message;
            while((message = consumer.Receive(TimeSpan.FromMilliseconds(2000))) != null)
            {
                var objectMessage = message as IObjectMessage;
                if(objectMessage != null)
                {
                    tchat = objectMessage.Body as Tchat;
                    if (tchat != null)
                    {
                        textBox2.Text += string.Format("{0}{1}", tchat.Message, Environment.NewLine);
                    }
                }
            }
        }
    }

If I close my windows form and restart it, then my label is well updated but I don’t want to close it and re open it.

Do you have any ideas guys ?

Answer 1

Try creating a class with an event delegate like this.

A subscriber class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Apache.NMS;
using Apache.NMS.ActiveMQ;
using Apache.NMS.ActiveMQ.Commands;

namespace Utilities
{
    public delegate void QMessageReceivedDelegate(string message);
    public class MyQueueSubscriber : IDisposable
    {
        private readonly string topicName = null;
        private readonly IConnectionFactory connectionFactory;
        private readonly IConnection connection;
        private readonly ISession session;
        private readonly IMessageConsumer consumer;
        private bool isDisposed = false;
        public event QMessageReceivedDelegate OnMessageReceived;

        public MyQueueSubscriber(string queueName, string brokerUri, string clientId)
        {
            this.topicName = queueName;
            this.connectionFactory = new ConnectionFactory(brokerUri);
            this.connection = this.connectionFactory.CreateConnection();
            this.connection.ClientId = clientId;
            this.connection.Start();
            this.session = connection.CreateSession();
            ActiveMQQueue topic = new ActiveMQQueue(queueName);
            //this.consumer = this.session.CreateDurableConsumer(topic, consumerId, "2 > 1", false);
            this.consumer = this.session.CreateConsumer(topic, "2 > 1");
            this.consumer.Listener += new MessageListener(OnMessage);

        }

        public void OnMessage(IMessage message)
        {
            ITextMessage textMessage = message as ITextMessage;
            if (this.OnMessageReceived != null)
            {
                this.OnMessageReceived(textMessage.Text);
            }
        }

        #region IDisposable Members

        public void Dispose()
        {
            if (!this.isDisposed)
            {
                this.consumer.Dispose();
                this.session.Dispose();
                this.connection.Dispose();
                this.isDisposed = true;
            }
        }

        #endregion

    }
}

Winforms
In your windows form Subscribe to the queue like this

    MyQueueSubscriber QueueSubscriber = new MyQueueSubscriber(QueueName, ActiveMQHost, QueueClientId);
    QueueSubscriber.OnMessageReceived += new QMessageReceivedDelegate(QueueSubscriber_OnMessageReceived);

static void QueueSubscriber_OnMessageReceived(string message)
{
        SetText(message);
}

    private void SetText(string text)
    {
        // InvokeRequired required compares the thread ID of the
        // calling thread to the thread ID of the creating thread.
        // If these threads are different, it returns true.
        if (this.textBox1.InvokeRequired)
        {   
            SetTextCallback d = new SetTextCallback(SetText);
            this.Invoke(d, new object[] { text });
        }
        else
        {
            this.labelname.value = text;
        }
    }

Resources:
Unfortunately there are not that many resources to teach C# & ActiveMQ. Try using http://activemq.apache.org/nms/ as this was quite good.

Try looking at a small article from http://www.codersource.net/MicrosoftNet/CAdvanced/PublishSubscribeinCusingActiveMQ.aspx. Disclaimer: This is my website and the article was written by me. Sorry for the self publicity. But I feel this is relevant to the topic.