MQTT服务器订阅消息例子

using MQTTnet;
using MQTTnet.Client;
using MQTTnet.Packets;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Sample_MQTT_Client
{
    public partial class Form1 : Form
    {
        IMqttClient mqttClient;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            ReceiveData();
        }

        public async void ReceiveData() 
        {
            //不等空，断开连接
            if (mqttClient == null) {
                var factory = new MqttFactory();
                mqttClient = factory.CreateMqttClient();
                var options = new MqttClientOptionsBuilder()
                    .WithTcpServer("192.168.240.53", 1883)
                    .Build();

                await mqttClient.ConnectAsync(options);

                var subOption = new MqttClientSubscribeOptions()
                {
                    TopicFilters = new List<MqttTopicFilter> 
                    { 
                        new MqttTopicFilterBuilder()
                        .WithTopic("ShuttleLoom")
                        .WithQualityOfServiceLevel(MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce)
                        .Build()
                    }
                };

                await mqttClient.SubscribeAsync(subOption);
                mqttClient.ApplicationMessageReceivedAsync += MqttClient_ApplicationMessageReceivedAsync;
            }
            else {
                await mqttClient.DisconnectAsync();
            }
        }

        private Task MqttClient_ApplicationMessageReceivedAsync(MqttApplicationMessageReceivedEventArgs arg)
        {
            try
            {
                string data = arg.ApplicationMessage.ConvertPayloadToString();
                string strdata = "\n获得数据：" + "\n" + data + "\n";

                //this.txtData.Text = strdata;

                this.txtData.Invoke(
                               new Action(() =>
                               {
                                   this.txtData.Text += strdata;
                               }));
            }
            catch (Exception)
            {

            }

            return null;
        }

        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            Application.Exit();
        }
    }
}