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;   
            });
        }




    }
}

Hello, I got an error for this line:

        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;  

"name dispatcher does not exist", what to do?

@BeginnerRaffe: Are you using WPF or Winforms? Is you are using winforms, you can replace

  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; 

with:

txtReceived.Invoke((MethodInvoker)(() => txtReceived.Text = ReceivedMessage));

Hii, My error is Severity Code Description Project File Line Suppression State
Error CS0246 "The type or namespace name 'uPLibrary' could not be found" (are you missing a using directive or an assembly reference?) First C:\Users\Home\source\repos\First\First\MainWindow.xaml.cs 18 Active
I am using 2019 version, Can you plss say the solution for this??

Hi Christian, i need uPLibrary same as a dll. can i use it that way

Hi,
I am using M2qtt service and client for my window application. due to some reason my client is getting disconnected from the service. but in server side,the service is running correctly. If I restart my client application, it is again started working correctly. Is there any way in which I can trace the reason of disconnecting my client from service? How how to fire the disconnect event if my client is getting disconnect from service?
Thanks, Ashok

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

namespace IOTWEBSITE
{
public partial class Default : System.Web.UI.Page
{
delegate void SetTextCallback(string text);
MqttClient client;
string clientId;
protected void Page_Load(object sender, EventArgs e)
{

        client = new MqttClient("broker.hivemq.com");
        client.MqttMsgPublishReceived += client_MqttMsgPublishReceived;
        clientId = Guid.NewGuid().ToString();
        client.Connect(clientId);
    }
    void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)

    {

        string ReceivedMessage = Encoding.UTF8.GetString(e.Message);
        //TextBox2.Text = ReceivedMessage;       
        SetText(ReceivedMessage);

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string Topic = "testtopic/tanny";
        client.Publish(Topic, Encoding.UTF8.GetBytes(TextBox1.Text), MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE, true);
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        string Topic = "testtopic/tanny";
        client.Subscribe(new string[] { Topic }, new byte[] { 0 });
        SetText("");

    }
    private void SetText(string text)
    {

        SetTextCallback d = new SetTextCallback(SetText);
        this.Invoke(d, new object[] { text });                                      /// Invoke Error Occured  (How to Remove)
        TextBox3.Text = text;

    }
}

}

same thing windows application working fine
but when use web application then invoke error occured
(message send on hive mqtt broker but did not receive any message )
last 3 days finding solution
please help ................

Thanks, but probably not according to this article: https://mosquitto.org/man/mqtt-7.html Am Mi., 9. Sept. 2020 um 10:10 Uhr schrieb Poteis <notifications@github.com

…

: ***@***.**** commented on this gist. ------------------------------ As far as my knowledge goes you need to start from a root ("/") and not just with the topic name. May change "testtopic/tanny" to "/testtopic/tanny" and make sure you subscribe the same topic — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://gist.github.com/7b5117dca561c01def041e7d4c6d2771#gistcomment-3447077>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAJCDLVOGCO3XXAX6XNVTM3SE42BDANCNFSM4IIC52AQ> .

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 ?