We always see Python or Node.js examples in IoT, but C# is just as easy, robust, and secure. In this quick tutorial we will:
- Connect our .NET client to a public broker, like: HiveMQ.
- Subscribe to a topic:
iot/door/status. - Display incoming messages in the console.
What you need
- .NET 8 SDK
- The MQTTnet library
- A public MQTT broker (
broker.hivemq.com:1883) - And a willingness to automate and experiment!
Example code
using MQTTnet; using MQTTnet.Client; using MQTTnet.Client.Options; using System; using System.Text; using System.Threading.Tasks; class Program { static async Task Main() { // 1. Configure client options var options = new MqttClientOptionsBuilder() .WithTcpServer("broker.hivemq.com", 1883) .WithClientId("dotnet-iot-demo") .Build(); // 2. Create the client and define handlers var factory = new MqttFactory(); var client = factory.CreateMqttClient(); client.UseConnectedHandler(async _ => { Console.WriteLine("Connected to HiveMQ"); await client.SubscribeAsync("iot/door/status"); Console.WriteLine("Subscribed to: iot/door/status"); }); client.UseApplicationMessageReceivedHandler(e => { var payload = Encoding.UTF8.GetString(e.ApplicationMessage.Payload); Console.WriteLine($"Message received: {payload}"); // Here you could, for example: // • Log the event to your database // • Trigger an email or SMS alert // • Send the data to a web dashboard }); // 3. Connect and wait for messages await client.ConnectAsync(options); Console.WriteLine("Press ENTER to exit..."); Console.ReadLine(); } } 
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