前言：

MQTT是IBM开发的一个即时通讯协议。MQTT是面向M2M和物联网的连接协议，采用轻量级发布和订阅消息传输机制。

大家可以直接上GitHub下载MQQT服务的源码，源码地址：https://github.com/mqtt/mqtt.github.io/wiki/libraries

主要内容：

官方文档翻译：

M2Mqtt库提供了一个主类MqttClient，代表连接到代理的MQTT客户端。您可以连接到提供其IP地址或主机名的代理，以及可选的与MQTT协议相关的一些参数。

连接到代理后，您可以使用Publish（）方法向主题和Subscribe（）方法发布消息以订阅主题并接收其上发布的消息。

MqttClient类是基于事件，以便您在邮件发布到您订阅的主题时收到一个事件。消息发布完成后，您可以收到事件，您已订阅或取消订阅主题。

以客户端为主题的例子：

...

// create client instance 
MqttClient client = new MqttClient(IPAddress.Parse(MQTT_BROKER_ADDRESS));

// register to message received 
client.MqttMsgPublishReceived += client_MqttMsgPublishReceived;

string clientId = Guid.NewGuid().ToString(); 
client.Connect(clientId);

// subscribe to the topic "/home/temperature" with QoS 2 
client.Subscribe(new string[] { "/home/temperature" }, new byte[] { MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE });

...

static void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e) 
{ 
// handle message received 
}

一般C#客户端都是应用单例模式，下面的是我封装的类：

public class MqttClientService

{

private static volatile MqttClientService _instance = null;

private static readonly object LockHelper = new object();

/// <summary>

/// 创建单例模式

/// </summary>

/// <param name="ipAddress"></param>

/// <returns></returns>

public static MqttClientService CreateInstance(string ipAddress)

{

if (_instance == null)

{

lock (LockHelper)

{

if (_instance == null)

_instance = new MqttClientService(ipAddress);

}

}

return _instance;

}

/// <summary>

/// 实例化订阅客户端

/// </summary>

public MqttClient SubscribeClient { get; set; }

public Action<Object, MqttMsgPublishEventArgs> ClientPublishReceivedAction { get; set; }

public MqttClientService(string ipAddress)

{

// create client instance

SubscribeClient = new MqttClient(IPAddress.Parse(ipAddress));

// register to message received

SubscribeClient.MqttMsgPublishReceived += client_MqttMsgPublishReceived;

string clientId = Guid.NewGuid().ToString();

SubscribeClient.Connect(clientId);

// subscribe to the topic "/home/temperature" with QoS 2

SubscribeClient.Subscribe(new string[] { "avatar/uploaded" }, new byte[] { MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE });

}

void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)

{

// handle message received

ClientPublishReceivedAction.Invoke(sender, e);

}

public void client_MqttMsgPublish(string publishString)

{

SubscribeClient.Publish("avatar/signed", Encoding.UTF8.GetBytes(publishString), MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE, false);

}

}

用户只需要把订阅的路径写到Subscribe即可。

相关文章：

• 使用 MQTTnet 快速实现 MQTT 通信

原文地址: https://www.cnblogs.com/dongqinnanren/p/6839319.html

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