添加了事件服务，并完成了设备状态改变后写入数据库

DMS.Application/Events/MqttConnectionChangedEventArgs.cs

@@ -0,0 +1,50 @@
+using System;
+
+namespace DMS.Application.Events;
+
+/// <summary>
+/// MQTT连接状态改变事件参数
+/// </summary>
+public class MqttConnectionChangedEventArgs : EventArgs
+{
+    /// <summary>
+    /// MQTT服务器ID
+    /// </summary>
+    public int MqttServerId { get; }
+
+    /// <summary>
+    /// MQTT服务器名称
+    /// </summary>
+    public string MqttServerName { get; }
+
+    /// <summary>
+    /// 旧连接状态
+    /// </summary>
+    public bool OldConnectionStatus { get; }
+
+    /// <summary>
+    /// 新连接状态
+    /// </summary>
+    public bool NewConnectionStatus { get; }
+
+    /// <summary>
+    /// 状态改变时间
+    /// </summary>
+    public DateTime ChangeTime { get; }
+
+    /// <summary>
+    /// 初始化MqttConnectionChangedEventArgs类的新实例
+    /// </summary>
+    /// <param name="mqttServerId">MQTT服务器ID</param>
+    /// <param name="mqttServerName">MQTT服务器名称</param>
+    /// <param name="oldStatus">旧连接状态</param>
+    /// <param name="newStatus">新连接状态</param>
+    public MqttConnectionChangedEventArgs(int mqttServerId, string mqttServerName, bool oldStatus, bool newStatus)
+    {
+        MqttServerId = mqttServerId;
+        MqttServerName = mqttServerName;
+        OldConnectionStatus = oldStatus;
+        NewConnectionStatus = newStatus;
+        ChangeTime = DateTime.Now;
+    }
+}