ASP.NET MQTT 客户端通信

前期准备

本篇文章采用的Mqtt 2.8.5类库    Visual Studio2019

引用mqtt类库

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


了解MQTT常用事件以及属性

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）

了解Qos 消息等级

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()}====");
}