MQTT,IBM发明的物联网通讯协议基于tcp ip , 收集传感器上的数据。
下图理解： broker 这里有很多消息，根据主题不同来进行区分，它这里可以保管所有连过来的客户端的数据，然后客户端，通过订阅broker它有的主题进行获取数据。
学习网址：https://github.com/chkr1011/MQTTnet/wiki/Client
broker网址 代理：http://www.mqtt-dashboard.com/
开发(只需客户端)：
vs2015
1.添加引用本文MQTTnet2.8.4（管理NuGet程序包）
2.界面
3.代码
using MQTTnet;using MQTTnet.Client;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 server{ ???public partial class Form1 : Form ???{ ???????public Form1() ???????{ ???????????InitializeComponent(); ???????} ???????public static IMqttClient mqttClient = null; ???????public static IMqttClientOptions options = null; ???????private void Form1_Load(object sender, EventArgs e) ???????{ ???????????//实例化对象 ???????????var factory = new MqttFactory(); ???????????mqttClient = factory.CreateMqttClient(); ???????????mqttClient.Connected += SubscribeTopic; ???????????mqttClient.Disconnected += MqttClient_Disconnected; ???????????mqttClient.ApplicationMessageReceived += Receive; ???????????//配置参数 ???????????//options = new MqttClientOptionsBuilder() ???????????// ???.WithClientId(Guid.NewGuid().ToString().Substring(0, 5)) ???????????// ???.WithTcpServer("broker.hivemq.com") ???????????// ???.WithCredentials("bud", "%spencer%") ???????????// ???.WithTls() ???????????// ???.WithCleanSession() ???????????// ???.Build(); ???????????options = new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").Build(); ???????????//连接 ???????????Task.Run(async () => { await ConnectMqtt(); }); ???????} ???????public async Task ConnectMqtt() ???????{ ???????????try ???????????{ ???????????????MqttClientConnectResult x = await mqttClient.ConnectAsync(options); ???????????} ???????????catch (Exception ex) ???????????{ ???????????????Invoke((new Action(() => ???????????????{ ???????????????????textBox2.Text = $"连接到MQTT服务器失败！" + Environment.NewLine + ex.Message + Environment.NewLine; ???????????????}))); ???????????} ???????} ???????//接收消息 ???????public async void Receive(object sender, MqttApplicationMessageReceivedEventArgs e) ???????{ ???????????try ???????????{ ???????????????Invoke((new Action(() => ???????????????{ ???????????????????//textBox2.AppendText("### RECEIVED APPLICATION MESSAGE 接收消息 ###"); ???????????????????textBox2.AppendText($"Topica(主题) = {e.ApplicationMessage.Topic}" + "\t\n"); ???????????????????textBox2.AppendText($"Payloada(内容) = {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}" + "\t\n"); ???????????????????//textBox2.AppendText($"+ QoS = {e.ApplicationMessage.QualityOfServiceLevel}"); ???????????????????//textBox2.AppendText($"+ Retain = {e.ApplicationMessage.Retain}"); ???????????????}))); ???????????} ???????????catch (Exception ex) ???????????{ ???????????????Invoke((new Action(() => ???????????????{ ???????????????????textBox2.Text = ex.Message; ???????????????}))); ???????????} ???????} ???????//连接成功 ???????public async void SubscribeTopic(object sender, EventArgs e) ???????{ ???????????Invoke((new Action(() => { label2.Text = "连接成功"; }))); ???????} ???????????????/// <summary> ???????/// 连接失败 ???????/// </summary> ???????/// <param name="sender"></param> ???????/// <param name="e"></param> ???????public async void MqttClient_Disconnected(object sender, EventArgs e) ???????{ ???????????Invoke((new Action(() => ???????????{ ???????????????textBox2.AppendText("连接失败！" + Environment.NewLine); ???????????}))); ???????????//重新连接 ???????????await Task.Delay(TimeSpan.FromSeconds(3)); ???????????try ???????????{ ???????????????await mqttClient.ConnectAsync(options); ???????????????Invoke((new Action(() => ???????????????{ ???????????????????textBox2.AppendText("连接成功！"); ???????????????}))); ???????????} ???????????catch ???????????{ ???????????????Invoke((new Action(() => ???????????????{ ???????????????????textBox2.AppendText("连接失败！"); ???????????????}))); ???????????} ???????} ???????/// <summary> ???????/// 订阅消息 ???????/// </summary> ???????/// <param name="sender"></param> ???????/// <param name="e"></param> ???????private void button1_Click(object sender, EventArgs e) ???????{ ???????????string topic = textBox1.Text; ???????????mqttClient.SubscribeAsync(new TopicFilterBuilder().WithTopic(topic).Build()); ???????????textBox2.AppendText("### 订阅" + topic + "成功 ###\t\n"); ???????} ???????/// <summary> ???????/// 释放资源 ???????/// </summary> ???????/// <param name="sender"></param> ???????/// <param name="e"></param> ???????private void button2_Click(object sender, EventArgs e) ???????{ ???????????mqttClient.Dispose(); ???????????textBox2.AppendText("### 断开连接###\t\n"); ???????} ???????/// <summary> ???????/// 发布一个主题内容 ???????/// </summary> ???????/// <param name="sender"></param> ???????/// <param name="e"></param> ???????private void button3_Click(object sender, EventArgs e) ???????{ ???????????var message = new MqttApplicationMessageBuilder() ???????????????.WithTopic(textBox3.Text) ???????????????.WithPayload(textBox4.Text) ???????????????.WithExactlyOnceQoS() ???????????????.WithRetainFlag() ???????????????.Build(); ????????????mqttClient.PublishAsync(message); ???????} ???}}4.运行效果
这些数据就是根据你的主题从http://www.mqtt-dashboard.com/ 代理取来，你也可以发布主题的内容，别人也可以订阅你的主题，取数据。
MqttNet 通讯
原文地址：https://www.cnblogs.com/Evan-Pei/p/9816545.html