C# mqttnet 客户端发布与订阅实例

在C#中，使用MqttNet库进行MQTT（Message Queuing Telemetry Transport）客户端的发布（Publish）和订阅（Subscribe）操作非常直观。首先，你需要安装`Mqttnet` NuGet包。下面是一个简单的示例：

using MqttNet;
using System.Threading.Tasks;

// 创建MQTT连接选项
var options = new MqttClientOptionsBuilder()
    .WithTcpServer("your_mqtt_broker_url")
    .Build();

// 创建MQTT客户端
var mqttClient = new MqttClient(options);

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

// 发布消息到主题 (Topic)
public async Task Publish(string topic, string message)
{
    var publishMessage = new MqttApplicationMessageBuilder()
        .WithTopic(topic)
        .WithPayload(message)
        .WithExactlyOnceQoS()
        .Build();
    await mqttClient.PublishAsync(publishMessage);
}

// 订阅特定主题并处理消息
public async Task SubscribeAndHandle(string subscriptionTopic)
{
    var receivedEvent = new MqttReceivedEventArgs { Topic = subscriptionTopic };

    // 使用回调处理接收到的消息
    mqttClient.UseApplicationMessageReceivedHandler(async e =>
    {
        receivedEvent.ApplicationMessage = e.ApplicationMessage;
        Console.WriteLine($"Received on {e.Topic}: {e.ApplicationMessage.Payload}");
    });

    // 订阅主题
    await mqttClient.SubscribeAsync(new[] { subscriptionTopic });
}

// 断开连接
async Task Disconnect()
{
    await mqttClient.DisconnectAsync();
}

// 调用这些方法来完成发布、订阅和断开连接的操作
// ...

在这个例子中，`Publish`方法用于发送数据到指定的主题，而`SubscribeAndHandle`方法则订阅主题，并通过`UseApplicationMessageReceivedHandler`设置接收消息的处理函数。