mycorerepository/MyCore/Services/MQTTService.cs

using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Client.Options;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace MyCore.Services
{
    public class MQTTService
    {

        private IMqttClient _client;
        private IMqttClientOptions _options;
        private string _mqttServer = "192.168.31.140";
        private string _user = "mqtt";
        private string _password = "mqtt";

        // It's here to have the mqtt initialisation + logic for payload.. 

        // Related to which event occurs, a specific action is done.

        public MQTTService()
        {
            try
            {
                // Create a new MQTT client.
                _client = new MqttFactory().CreateMqttClient();

                _options = new MqttClientOptionsBuilder()
                    .WithClientId("ApiService")
                    .WithTcpServer(_mqttServer)
                    .WithCredentials(_user, _password)
                    .WithCleanSession()
                    .Build();

                _client.ConnectAsync(_options, CancellationToken.None).ContinueWith(res => {
                    if (res.Status == TaskStatus.RanToCompletion)
                    {
                        Console.WriteLine("It's connected");
                    }
                    else
                    {
                        Console.WriteLine($"Error connecting to {_mqttServer}");
                    }
                });

                _client.UseDisconnectedHandler(async e =>
                {
                    Console.WriteLine("### DISCONNECTED FROM SERVER ###");
                    await Task.Delay(TimeSpan.FromSeconds(5));

                    try
                    {
                        await _client.ConnectAsync(_options, CancellationToken.None); // Since 3.0.5 with CancellationToken
                    }
                    catch
                    {
                        Console.WriteLine("### RECONNECTING FAILED ###");
                    }
                });

                _client.UseConnectedHandler(async e =>
                {
                    Console.WriteLine("### CONNECTED WITH SERVER ###");

                    // Subscribe to a topic
                    await _client.SubscribeAsync(new TopicFilterBuilder().WithTopic("#").Build());

                    Console.WriteLine("### SUBSCRIBED ###");
                });


                _client.UseApplicationMessageReceivedHandler(e =>
                {
                    Console.WriteLine("### RECEIVED APPLICATION MESSAGE ###");
                    Console.WriteLine($"+ Topic = {e.ApplicationMessage.Topic}");
                    Console.WriteLine($"+ Payload = {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}");
                    Console.WriteLine($"+ QoS = {e.ApplicationMessage.QualityOfServiceLevel}");
                    Console.WriteLine($"+ Retain = {e.ApplicationMessage.Retain}");
                    Console.WriteLine();
                });


            }
            catch (Exception e)
            {
                Console.WriteLine($"Error during creation of MQTTService with {_mqttServer}, exceptions : {e}");
            }

        }

        public async void PublishMessage(string topic, string message)
        {
            var mqttMessage = new MqttApplicationMessageBuilder()
                .WithTopic(topic)
                .WithPayload(message)
                .WithExactlyOnceQoS()
                .WithRetainFlag()
                .Build();

            await _client.PublishAsync(mqttMessage);
        }

        /*protected async Task Start()
        {
            var server = new MqttFactory().CreateMqttServer();

            try
            {
                var client1 = new MqttFactory().CreateMqttClient();
                await client1.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer(_mqttServer).Build());
                var message = new MqttApplicationMessageBuilder().WithPayload("It's a test").WithTopic("IpAddress").WithRetainFlag().Build();
                await client1.PublishAsync(message);

                await Task.Delay(500);

            }
            finally
            {
                await server.StopAsync();
            }
        }*/

    }
}