C# MQTTnet使用心得和C# MQTT库M2Mqtt的使用方法

1.MQTTnet开源库，https://github.com/chkr1011/MQTTnet

MQTTnet.dll 2.8.5 下载

链接：https://pan.baidu.com/s/1BjQ41vOqQ6-JoY06m2uN4Q
提取码：a18s
（此版本示例：https://download.csdn.net/download/uaime/11359429 我尝试升级版本，很多方法不支持，没耐心看文档）

知识点（关于MQTT的详细说明 http://x5zj.com/?p=42）

2.服务器端和客户端（看上实例下载）

服务器端和客户端两个，他们需要保持长连接，主要是通过订阅和发布来进行消息的传递交换。

MQTT 服务端主要用于与多个客户端保持连接，并处理客户端的发布和订阅等逻辑。一般很少直接从服务端发送消息给客户端（可以使用 mqttServer.Publish(appMsg); 直接发送消息），多数情况下服务端都是转发主题匹配的客户端消息，在系统中起到一个中介的作用。

而客户端主要是通过向服务端订阅它感兴趣（主题）的消息，另一些客户端向服务端发布（主题）消息，服务端将订阅和发布的主题进行匹配，并将消息转发给匹配通过的客户端。

3连接，通信

（1）服务器端启动服务：

public static IMqttServer mqttServer = null; //创建对象

// 配置一个mqtt服务.
var optionsBuilder = new MqttServerOptionsBuilder()
//连接记录数，默认一般为2000
.WithConnectionBacklog(2000)
//服务器连接端口
.WithDefaultEndpointPort(port)
//连接验证器
.WithConnectionValidator(ValidatingMqttClients())
//持续会话
.WithPersistentSessions()

;
// 建立一个MQTT服务.
mqttServer = new MqttFactory().CreateMqttServer();
mqttServer.ApplicationMessageReceived += MqttServer_ApplicationMessageReceived;
mqttServer.ClientSubscribedTopic += MqttServer_ClientSubscribedTopic;
mqttServer.ClientUnsubscribedTopic += MqttServer_ClientUnsubscribedTopic;
mqttServer.ClientConnected += MqttServer_ClientConnected;
mqttServer.ClientDisconnected += MqttServer_ClientDisconnected;

//启动mqtt服务
await Task.Run(async () => { await mqttServer.StartAsync(optionsBuilder.Build()); });

（2）客户端

与服务器端连接

连接语句：

private IMqttClient mqttClient = null; //客户端对象

//实例化创建客户端对象
var Factory = new MqttFactory();
mqttClient = Factory.CreateMqttClient();
mqttClient.ApplicationMessageReceived += MqttClient_ApplicationMessageReceived;
mqttClient.Connected += MqttClient_Connected;
mqttClient.Disconnected += MqttClient_Disconnected;

//调用异步方法连接到服务端

await mqttClient.ConnectAsync(option());

option的信息设置：

public IMqttClientOptions option()
{
//连接到服务器前，获取所需要的MqttClientTcpOptions 对象的信息
var options = new MqttClientOptionsBuilder()
.WithClientId(ClientId) // clientid是设备id
.WithTcpServer(IP, Port) //onenet ip：183.230.40.39 port:6002
.WithCredentials(UserName,pwd) //username为产品id 密码为鉴权信息或者APIkey
//.WithTls()//服务器端没有启用加密协议，这里用tls的会提示协议异常
.WithCleanSession(false)
.WithKeepAlivePeriod(TimeSpan.FromSeconds(2000))
.Build();
return options;
}

服务端支持 ClientConnected、ClientDisconnected 和 ApplicationMessageReceived 事件，分别用来检查客户端连接、客户端断开以及接收客户端发来的消息。

客户端支持 Connected、Disconnected 和 ApplicationMessageReceived 事件，用来处理客户端与服务端连接、客户端从服务端断开以及客户端收到消息的事情。

通过 mqtt接入onenet，其实也就是把onenet 平台当做mqtt broker，连接上稍作改变就可以了。

客户端（接收服务推送）封装类参考：

MQQT服务的源码，下载源码地址：https://github.com/mqtt/mqtt.github.io/wiki/libraries

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);//订阅时修改路径（主题）即可// 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);}}

C#mqtt库M2Mqtt的使用方法

目前最好用的C#库是 eclipse出的M2Mqtt库，

主页链接： http://www.eclipse.org/paho/clients/dotnet/

项目的地址是 https://github.com/eclipse/paho.mqtt.m2mqtt

使用方式是在vs 的命令中输入 Install-Package M2Mqtt

...

// create client instance
MqttClient client = new MqttClient(IPAddress.Parse(MQTT_BROKER_ADDRESS)); //注意是域名哦不支持IP

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

string strValue = Convert.ToString(value);

// publish a message on "/home/temperature" topic with QoS 2
client.Publish("/home/temperature", Encoding.UTF8.GetBytes(strValue), MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE, false);
然而，却存在一个坑， MQTT_BROKER_ADDRESS 不能用IP地址，而要用域名，用IP地址会出现在Connect这一步连接失败。

放一个示例，可以直接使用的。

https://sdk.bce.baidu.com/console-sdk/mqtt-net.rar?responseContentDisposition=attachment

这个是百度云mqtt物接入的一个例子，用的是mqtt协议，下载后，把域名改一下，就可以用了。

mqtt服务器可以采用http://mosquitto.org/download/ 实现的mosquitto服务器。

Source

mosquitto-1.6.3.tar.gz (319kB) (GPG signature)
Git source code repository (github.com)

Older downloads are available at https://mosquitto.org/files/

Windows

mosquitto-1.6.3-install-windows-x64.exe (~1.4 MB) (64-bit build, Windows Vista and up, built with Visual Studio Community 2017)
mosquitto-1.6.3-install-windows-x32.exe (~1.4 MB) (32-bit build, Windows Vista and up, built with Visual Studio Community 2017)

组件下载：M2Mqtt.Net.dll （v4.3.0最新版 2019.7.16本地生成）

链接：https://pan.baidu.com/s/1lacs13v9nde8d2wrj2oU4g
提取码：l8cg

相关代码摘要：

//创建客户端实例（两种方式选择，否则出错，域名需转换）
MqttClient client = new MqttClient(IPAddress.Parse(MQTT_BROKER_ADDRESS)); //主机为IP时
MqttClient client = new MqttClient(MQTT_BROKER_ADDRESS); //当主机地址为域名时// 注册消息接收处理事件，还可以注册消息订阅成功、取消订阅成功、与服务器断开等事件处理函数
client.MqttMsgPublishReceived += client_MqttMsgPublishReceived; //生成客户端ID并连接服务器
string clientId = Guid.NewGuid().ToString();
client.Connect(clientId); // 订阅主题"/home/temperature" 消息质量为 2
// 三种参数：0 至多1次，1 至少1次，2 只有1次 （好像3保留）
client.Subscribe(new string[] { "/home/temperature" }, new byte[] { MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE }); ... void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
{
//处理接收到的消息
string msg = System.Text.Encoding.Default.GetString(e.Message);textBox1.AppendText("收到消息:" + msg + "\r\n");
} //**************************************************************// 发布消息到主题 "/home/temperature" 消息质量为 2,不保留
client.Publish("/home/temperature", Encoding.UTF8.GetBytes("hello"), MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE, false);

客户端代码参考2

服务端搭建：apache-apollo-***-windows，下载链接：http://activemq.apache.org/apollo/download.html

解压：在 apache-apollo bin文件夹中，作如下操作：

输入：apollo.cmd create test 创建虚拟test服务器主机，在该文件夹下会生成一个test目录
进入 apache-apollo-1.7.1\bin\test\bin文件，开启服务器。
进入test目录下etc文件夹中，找到apollo.xml
打开浏览器：输入http://127.0.0.1:61680,任意一个都可以，即可进入管理的web界面，账户：admin ，密码：password
测试连接，打开mqtt用户客户端，查看服务器显示情况

using MQTTnet;
using MQTTnet.Core;
using MQTTnet.Core.Client;
using MQTTnet.Core.Packets;
using MQTTnet.Core.Protocol;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;namespace mqtt_client
{public partial class Form1 : Form{private MqttClient mqttClient = null;public Form1(){InitializeComponent();Task.Run(async () => { await ConnectMqttServerAsync(); });}private async Task ConnectMqttServerAsync(){if (mqttClient == null){mqttClient = new MqttClientFactory().CreateMqttClient() as MqttClient;mqttClient.ApplicationMessageReceived += MqttClient_ApplicationMessageReceived;mqttClient.Connected += MqttClient_Connected;mqttClient.Disconnected += MqttClient_Disconnected;}try{var options = new MqttClientTcpOptions{Server = "127.0.0.1",Port=61613,ClientId = Guid.NewGuid().ToString(),UserName = "admin",Password = "password",CleanSession = true};await mqttClient.ConnectAsync(options);}catch (Exception ex){Invoke((new Action(() =>{textBox2.AppendText($"连接到MQTT服务器失败！" + Environment.NewLine + ex.Message + Environment.NewLine);})));}}private void MqttClient_Connected(object sender, EventArgs e){Invoke((new Action(() =>{textBox2.AppendText("已连接到MQTT服务器！" + Environment.NewLine);})));}private void MqttClient_Disconnected(object sender, EventArgs e){Invoke((new Action(() =>{textBox2.AppendText("已断开MQTT连接！" + Environment.NewLine);})));}private void MqttClient_ApplicationMessageReceived(object sender, MqttApplicationMessageReceivedEventArgs e){Invoke((new Action(() =>{textBox2.AppendText($">> {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}{Environment.NewLine}");})));}private void button1_Click(object sender, EventArgs e){string topic = textBox1.Text.Trim();if (string.IsNullOrEmpty(topic)){MessageBox.Show("订阅主题不能为空！");return;}if (!mqttClient.IsConnected){MessageBox.Show("MQTT客户端尚未连接！");return;}mqttClient.SubscribeAsync(new List<TopicFilter> {new TopicFilter(topic, MqttQualityOfServiceLevel.AtMostOnce)});textBox2.AppendText($"已订阅[{topic}]主题" + Environment.NewLine);textBox1.Enabled = false;button1.Enabled = false;}private void button2_Click(object sender, EventArgs e){string topic = textBox4.Text.Trim();if (string.IsNullOrEmpty(topic)){MessageBox.Show("发布主题不能为空！");return;}string inputString = textBox3.Text.Trim();var appMsg = new MqttApplicationMessage(topic, Encoding.UTF8.GetBytes(inputString), MqttQualityOfServiceLevel.AtMostOnce, false);mqttClient.PublishAsync(appMsg);}private void Form1_Load(object sender, EventArgs e){Sunisoft.IrisSkin.SkinEngine skin = new Sunisoft.IrisSkin.SkinEngine{SkinFile = @"./RealOne.ssk"};}}
}

参考资料：

https://github.com/mqtt/mqtt.github.io/wiki/libraries

https://github.com/leytton/m2mqtt (此项目下载后依赖项很多出问题，尝试修改没弄成)

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