Example of a C# MQTT client

MQTT Client

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;


// including the M2Mqtt Library
using uPLibrary.Networking.M2Mqtt;
using uPLibrary.Networking.M2Mqtt.Messages;


namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {

        MqttClient client;
        string clientId;


        // this code runs when the main window opens (start of the app)
        public MainWindow()
        {
            InitializeComponent();

            string BrokerAddress = "test.mosquitto.org";
            
            client = new MqttClient(BrokerAddress);

            // register a callback-function (we have to implement, see below) which is called by the library when a message was received
            client.MqttMsgPublishReceived += client_MqttMsgPublishReceived;

            // use a unique id as client id, each time we start the application
            clientId = Guid.NewGuid().ToString();

            client.Connect(clientId);
        }


        // this code runs when the main window closes (end of the app)
        protected override void OnClosed(EventArgs e)
        {
            client.Disconnect();

            base.OnClosed(e);
            App.Current.Shutdown();
        }


        // this code runs when the button "Subscribe" is clicked
        private void btnSubscribe_Click(object sender, RoutedEventArgs e)
        {
            if (txtTopicSubscribe.Text != "")
            {
                // whole topic
                string Topic = "/ElektorMyJourneyIoT/" + txtTopicSubscribe.Text + "/test";

                // subscribe to the topic with QoS 2
                client.Subscribe(new string[] { Topic }, new byte[] { 2 });   // we need arrays as parameters because we can subscribe to different topics with one call
                txtReceived.Text = "";
            }
            else
            {
                System.Windows.MessageBox.Show("You have to enter a topic to subscribe!");
            }
        }


        // this code runs when the button "Publish" is clicked
        private void btnPublish_Click(object sender, RoutedEventArgs e)
        {    
            if (txtTopicPublish.Text != "")
            {
                // whole topic
                string Topic = "/ElektorMyJourneyIoT/" + txtTopicPublish.Text + "/test";

                // publish a message with QoS 2
                client.Publish(Topic, Encoding.UTF8.GetBytes(txtPublish.Text), MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE, true);
            }
            else
            {
                System.Windows.MessageBox.Show("You have to enter a topic to publish!");
            }
        }


        // this code runs when a message was received
        void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
        {
            string ReceivedMessage = Encoding.UTF8.GetString(e.Message);

            Dispatcher.Invoke(delegate {              // we need this construction because the receiving code in the library and the UI with textbox run on different threads
                txtReceived.Text = ReceivedMessage;   
            });
        }




    }
}

Ye my bad. Read that shortly after too. Although all the examples I saw started with the root "/"... Quiet the reason why i deleted that comment as it was unnecessary and wrong at that point. Sorry

hi I got error at txtTopicSubscribe.Text and other .Text like txtReceived, txtPublish and others. It says the name does not exist. Did I miss any using library? I only install m2mqtt Nuget package.

i tried this https://gist.github.com/cwschroeder/7b5117dca561c01def041e7d4c6d2771#gistcomment-2790033 but still same error.

hi I got error at txtTopicSubscribe.Text and other .Text like txtReceived, txtPublish and others. It says the name does not exist. Did I miss any using library? I only install m2mqtt Nuget package.

i tried this https://gist.github.com/cwschroeder/7b5117dca561c01def041e7d4c6d2771#gistcomment-2790033 but still same error.

in reply to this, i learned that those supposed .Text is where textbox should be linked. Sorry I'm a self-learnt newbie, just thought it would be useful to share here too

protected override void OnClosed(EventArgs e)
{
client.Disconnect();

        base.OnClosed(e);
        App.Current.Shutdown();
      
    }

In the above code App does not exist how to solve it please tell me.

protected override void OnClosed(EventArgs e)
{
client.Disconnect();

        base.OnClosed(e);
        App.Current.Shutdown();
      
    }

In the above code App does not exist how to solve it please tell me.

I think if you dont use any app in your program you can just exclude the code

if my broker return object ? how to handle this in the callback event ?