mqtt在公共网络通信 c#

MQTTnet是一个开源的MQTT库，可以在.NET平台上实现MQTT通信。它提供了一套简单易用的API，支持MQTT协议的连接、发布和订阅等功能。你可以使用MQTTnet来实现在C#中使用MQTT进行公共网络通信。

以下是一个使用MQTTnet库在C#中实现MQTT通信的示例：

using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Client.Options;
using MQTTnet.Extensions.ManagedClient;

public class MqttClientExample
{
    private static async Task Main()
    {
        var factory = new MqttFactory();
        var mqttClient = factory.CreateMqttClient();

        var options = new MqttClientOptionsBuilder()
            .WithTcpServer("broker.hivemq.com", 1883) // 设置MQTT服务器地址和端口
            .Build();

        mqttClient.UseConnectedHandler(async e =>
        {
            Console.WriteLine("Connected to MQTT broker!");

            // 订阅主题
            await mqttClient.SubscribeAsync(new MqttTopicFilterBuilder().WithTopic("topic/test").Build());
        });

        mqttClient.UseDisconnectedHandler(async e =>
        {
            Console.WriteLine("Disconnected from MQTT broker!");
            await Task.Delay(TimeSpan.FromSeconds(5));

            try
            {
                await mqttClient.ConnectAsync(options); // 重新连接
            }
            catch
            {
                Console.WriteLine("Reconnect failed!");
            }
        });

        mqttClient.UseApplicationMessageReceivedHandler(e =>
        {
            Console.WriteLine($"Received message: {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}");
        });

        await mqttClient.ConnectAsync(options); // 连接到MQTT服务器

        // 发布消息
        var message = new MqttApplicationMessageBuilder()
            .WithTopic("topic/test")
            .WithPayload("Hello MQTT")
            .WithExactlyOnceQoS()
            .WithRetainFlag()
            .Build();

        await mqttClient.PublishAsync(message);

        Console.ReadLine();

        await mqttClient.DisconnectAsync(); // 断开连接
    }
}

上述示例代码使用了MQTTnet库来创建一个MQTT客户端，并连接到MQTT服务器。它订阅了名为"topic/test"的主题，并在收到消息时打印出来。然后，它发布了一条消息到同样的主题。

请注意，你需要将`broker.hivemq.com`替换为你要连接的实际MQTT服务器的地址。