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：
1 public class MqttClientService
2 {
3
4 private static volatile MqttClientService _instance = null;
5
6 private static readonly object LockHelper = new object();
7
8 /// <summary>
9 /// 创建单例模式
10 /// </summary>
11 /// <param name="ipAddress"></param>
12 /// <returns></returns>
13 public static MqttClientService CreateInstance(string ipAddress)
14 {
15 if (_instance == null)
16 {
17 lock (LockHelper)
18 {
19 if (_instance == null)
20 _instance = new MqttClientService(ipAddress);
21 }
22 }
23 return _instance;
24 }
25
26 /// <summary>
27 /// 实例化订阅客户端
28 /// </summary>
29 public MqttClient SubscribeClient { get; set; }
30
31
32 public Action<Object, MqttMsgPublishEventArgs> ClientPublishReceivedAction { get; set; }
33
34 public MqttClientService(string ipAddress)
35 {
36 // create client instance
37 SubscribeClient = new MqttClient(IPAddress.Parse(ipAddress));
38
39 // register to message received
40 SubscribeClient.MqttMsgPublishReceived += client_MqttMsgPublishReceived;
41
42 string clientId = Guid.NewGuid().ToString();
43
44 SubscribeClient.Connect(clientId);
45
46 // subscribe to the topic "/home/temperature" with QoS 2
47 SubscribeClient.Subscribe(new string[] { "avatar/uploaded" }, new byte[] { MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE });
48 }
49
50 void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
51 {
52 // handle message received
53 ClientPublishReceivedAction.Invoke(sender, e);
54 }
55
56 public void client_MqttMsgPublish(string publishString)
57 {
58 SubscribeClient.Publish("avatar/signed", Encoding.UTF8.GetBytes(publishString), MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE, false);
59 }
60 }
用户只需要把订阅的路径写到Subscribe即可。