I am trying to go data from a Mqtt-broker but I have no glue how to implement this in c#. Has anybody a solution for my problem?

CodePudding user response：

I would suggest taking a look at MQTTnet, which is probably the most popular .Net (C#) MQTT client/server package out there. It is well documented and actively maintained.

https://github.com/chkr1011/MQTTnet

Examples of connecting to a broker can be found on their wiki at:

https://github.com/chkr1011/MQTTnet/wiki/Client

Update with example code:

using MQTTnet;
using MQTTnet.Client.Connecting;
using MQTTnet.Client.Disconnecting;
using MQTTnet.Client.Options;
using MQTTnet.Client.Receiving;
using MQTTnet.Extensions.ManagedClient;
using System;
using System.Threading.Tasks;

namespace ConsoleSubscriber
{
    class Program
    {
        static async Task Main()
        {
            var mqttClientId = "MyClientId";             // Unique ClientId or pass a GUID as string for something random
            var mqttBrokerAddress = "127.0.0.1";         // hostname or IP address of your MQTT broker
            var mqttBrokerUsername = "MyUsername";       // Broker Auth username if using auth
            var mqttBrokerPassword = "MyPassword";       // Broker Auth password if using auth
            var topic = "MyTopicOfData";                 // topic to subscribe to

            var mqttClient = new MqttFactory().CreateManagedMqttClient();
            var mqttClientOptions = new ManagedMqttClientOptionsBuilder()
                        .WithAutoReconnectDelay(TimeSpan.FromSeconds(5))
                        .WithClientOptions(new MqttClientOptionsBuilder()
                            .WithTcpServer(mqttBrokerAddress)
                            .WithClientId(mqttClientId)
                            .WithCredentials(mqttBrokerUsername, mqttBrokerPassword)     // Remove this line if no auth
                            .WithCleanSession()
                            .Build()
                        )
                        .Build();

            mqttClient.ApplicationMessageReceivedHandler = new MqttApplicationMessageReceivedHandlerDelegate(e => MqttOnNewMessage(e));
            mqttClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(e => MqttOnConnected(e));
            mqttClient.DisconnectedHandler = new MqttClientDisconnectedHandlerDelegate(e => MqttOnDisconnected(e));

            await mqttClient.SubscribeAsync(new MqttTopicFilterBuilder().WithTopic(topic).WithExactlyOnceQoS().Build());
            await mqttClient.StartAsync(mqttClientOptions);
        }

        private static void MqttOnNewMessage(MqttApplicationMessageReceivedEventArgs e)
        {
            // Do something with each incoming message from the topic

            Console.WriteLine($"MQTT Client: OnNewMessage Topic: {e.ApplicationMessage.Topic} / Message: {e.ApplicationMessage.Payload}");
        }

        private static void MqttOnConnected(MqttClientConnectedEventArgs e) => Console.WriteLine($"MQTT Client: Connected with result: {e.ConnectResult.ResultCode}");

        private static void MqttOnDisconnected(MqttClientDisconnectedEventArgs e) => Console.WriteLine($"MQTT Client: Broker connection lost with reason: {e.Reason}.");
    }
}