In the previous post, we worked with MQTTnet version 3, although version 4 of MQTTnet came in Jun 2022. As MQTTnet version 4 has a lot of changes, I thought it would be helpful to write a new article about developing a simple MQTT client using this version. To find more information on MQTT and what is MQTT client and broker please check this post.

Create a project

We need to create a console project. I use dotnet CLI to create a new project.

dotnet new console --name SimpleMQTTClient4

Now We have a new empty project to code an MQTT client.

Install Dependency

To work in dotnet with MQTT Client, we need to install the MQTTnet.Extensions.ManagedClient package from NuGet. This article uses version 4.

dotnet add package MQTTnet.Extensions.ManagedClient --version 4.0.2.221

Implementation

Open Program.cs.Add the below code.

using MQTTnet.Client;
using MQTTnet.Extensions.ManagedClient;
using MQTTnet;
using System.Text.Json;

IManagedMqttClient _mqttClient = new MqttFactory().CreateManagedMqttClient();

// Create client options object
MqttClientOptionsBuilder builder = new MqttClientOptionsBuilder()
                                        .WithClientId("behroozbc")
                                        .WithTcpServer("localhost");
ManagedMqttClientOptions options = new ManagedMqttClientOptionsBuilder()
                        .WithAutoReconnectDelay(TimeSpan.FromSeconds(60))
                        .WithClientOptions(builder.Build())
                        .Build();



// Set up handlers
_mqttClient.ConnectedAsync += _mqttClient_ConnectedAsync;


_mqttClient.DisconnectedAsync += _mqttClient_DisconnectedAsync;


_mqttClient.ConnectingFailedAsync += _mqttClient_ConnectingFailedAsync;


// Connect to the broker
await _mqttClient.StartAsync(options);

// Send a new message to the broker every second
while (true)
{
    string json = JsonSerializer.Serialize(new { message = "Hi Mqtt", sent = DateTime.UtcNow });
    await _mqttClient.EnqueueAsync("behroozbc.ir/topic/json", json);

    await Task.Delay(TimeSpan.FromSeconds(1));
}
Task _mqttClient_ConnectedAsync(MqttClientConnectedEventArgs arg)
{
    Console.WriteLine("Connected");
    return Task.CompletedTask;
};
Task _mqttClient_DisconnectedAsync(MqttClientDisconnectedEventArgs arg)
{
    Console.WriteLine("Disconnected");
    return Task.CompletedTask;
};
Task _mqttClient_ConnectingFailedAsync(ConnectingFailedEventArgs arg)
{
    Console.WriteLine("Connection failed check network or broker!");
    return Task.CompletedTask;
}

By default MQTT without encryption port is 1883. If you want to change it, add a parameter port number to WithTcpServer.

// Create the options for MQTT Broker
var options = new MqttServerOptionsBuilder()
    //Set endpoint to localhost
    .WithDefaultEndpoint()
    // Port is going to use 5004
    .WithDefaultEndpointPort(5004);

Conclusion

You have an MQTT client. I hope it was helpful. In this post, I will show you how to create a broker to test it.

You find this project on Github.

If you are still unsure of what to do or if you got any errors, I suggest you use the comment section below and let me know! I’m here to help.