ASP.NET MQTT 客户端通信第七秒-

本篇文章采用的Mqtt 2.8.5类库    Visual Studio2019

对着新建的项目右键，管理Nuget程序包，搜索MQTTNet选择版本2.8.5点击安装


Connected     连接成功事件
Disconnected     断开连接事件
ApplicationMessageReceived    订阅事件
ClientId    客户端ID（唯一）
Topic    订阅主题（一个客户端可以订阅一个到多个主题，接收到的主题消息由订阅接收消息事件处理）

mqtt消息等级称Qos分三个等级
MqttQualityOfServiceLevel.AtMostOnce    最多一次 MqttQualityOfServiceLevel.AtLeastOnce    最少一次 MqttQualityOfServiceLevel.ExactlyOnce    只有一次
注意：当qos=MqttQualityOfServiceLevel.AtLeastOnce或MqttQualityOfServiceLevel.ExactlyOnce的时候,就遇到问题了. 想让设备重新连接,获取到mqtt保存的消息,需要设置cleansession=false,就是设备每次登陆,都是用同一个session,而没有发出去的消息,是放在内存里面的,跟session关联,这里问题就大了.消息堆积,内存就挂了.所以有些 消息,需要自己业务逻辑处理或定期清理防止内存爆满

下面展示一些 内联代码片。

// mqtt客户端 private static MqttClient mqttClient; //ClientId，同SessionId性质一样，是客户端的身份识别唯一标识 public string ClientId=""; static void Main(string[] args) {  Console.WriteLine("===启动客户端MQTT===");  Console.Write("请输入ClientId:");     ClientId = Console.ReadLine().ToLower().Trim(); ConnectMqttService(); while (true) { if (mqttClient == null) { ConnectMqttService(); } } } public static void ConnectMqttService() { try { if (mqttClient == null || !mqttClient.IsConnected) {    mqttClient = new MqttFactory().CreateMqttClient() as MqttClient; //连接成功             mqttClient.Connected += MqttClient_Connected; //断开连接             mqttClient.Disconnected += MqttClient_Disconnected; //订阅客户端或服务端发布的消息             mqttClient.ApplicationMessageReceived += MqttClient_ApplicationMessageReceived; var options = new MqttClientOptions {     ClientId = ClientId,     CleanSession = true,     ChannelOptions = new MqttClientTcpOptions {      Server = "mqtt服务端ip地址",      Port = Convert.ToInt32(端口号) } };              Task.WaitAll(mqttClient.ConnectAsync(options)); MqttSubscribe(); } } catch (Exception ex) {   Console.WriteLine($"客户端ID标识为Client100001的消息连接MQTT服务器异常:" + ex.ToString()); } } //MQTT发布消息 content消息内容 public static void MqttClientPublish(String content) { var msg = new MqttApplicationMessage() {   Topic = "$Topic" + ClientId,   Payload = Encoding.UTF8.GetBytes(content), //QOS 消息等级   QualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce,   Retain = false };  mqttClient.PublishAsync(msg); } //订阅MQTT消息 public static void MqttSubscribe() {  mqttClient.SubscribeAsync(new List<TopicFilter> { new TopicFilter("$Topic"+ClientId,MqttQualityOfServiceLevel.AtMostOnce) }); } //订阅接收消息事件 private static void MqttClient_ApplicationMessageReceived(object sender, MqttApplicationMessageReceivedEventArgs e) { //订阅内容  String Payload = System.Text.Encoding.Default.GetString(e.ApplicationMessage.Payload);  Console.WriteLine($"===订阅消息：{e.ClientId}内容:{Payload}==="); } //mqtt断开连接两种形式 长时间订阅未接收到消息和服务端断开连接 private static void MqttClient_Disconnected(object sender, MqttClientDisconnectedEventArgs e) {  Console.WriteLine($"====已断开MQTT服务器，断开时间{DateTime.Now.ToString()}===="); } private static void MqttClient_Connected(object sender, MqttClientConnectedEventArgs e) {  Console.WriteLine($"=====连接MQTT服务器成功,连接时间{DateTime.Now.ToString()}===="); }