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/DeviceActiveChangedEventArgs.cs

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+using System;
+
+namespace DMS.Application.Events;
+
+/// <summary>
+/// 设备状态改变事件参数
+/// </summary>
+public class DeviceActiveChangedEventArgs : EventArgs
+{
+    /// <summary>
+    /// 设备ID
+    /// </summary>
+    public int DeviceId { get; }
+
+    /// <summary>
+    /// 设备名称
+    /// </summary>
+    public string DeviceName { get; }
+
+    /// <summary>
+    /// 旧状态
+    /// </summary>
+    public bool OldStatus { get; }
+
+    /// <summary>
+    /// 新状态
+    /// </summary>
+    public bool NewStatus { get; }
+
+    /// <summary>
+    /// 状态改变时间
+    /// </summary>
+    public DateTime ChangeTime { get; }
+
+    /// <summary>
+    /// 初始化DeviceStatusChangedEventArgs类的新实例
+    /// </summary>
+    /// <param name="deviceId">设备ID</param>
+    /// <param name="deviceName">设备名称</param>
+    /// <param name="oldStatus">旧状态</param>
+    /// <param name="newStatus">新状态</param>
+    public DeviceActiveChangedEventArgs(int deviceId, string deviceName, bool oldStatus, bool newStatus)
+    {
+        DeviceId = deviceId;
+        DeviceName = deviceName;
+        OldStatus = oldStatus;
+        NewStatus = newStatus;
+        ChangeTime = DateTime.Now;
+    }
+}

DMS.Application/Events/MqttConnectionChangedEventArgs.cs

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+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;
+    }
+}

DMS.Application/Events/VariableValueChangedEventArgs.cs

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+using System;
+
+namespace DMS.Application.Events;
+
+/// <summary>
+/// 变量值改变事件参数
+/// </summary>
+public class VariableValueChangedEventArgs : EventArgs
+{
+    /// <summary>
+    /// 变量ID
+    /// </summary>
+    public int VariableId { get; }
+
+    /// <summary>
+    /// 变量名称
+    /// </summary>
+    public string VariableName { get; }
+
+    /// <summary>
+    /// 旧值
+    /// </summary>
+    public string OldValue { get; }
+
+    /// <summary>
+    /// 新值
+    /// </summary>
+    public string NewValue { get; }
+
+    /// <summary>
+    /// 值改变时间
+    /// </summary>
+    public DateTime ChangeTime { get; }
+
+    /// <summary>
+    /// 初始化VariableValueChangedEventArgs类的新实例
+    /// </summary>
+    /// <param name="variableId">变量ID</param>
+    /// <param name="variableName">变量名称</param>
+    /// <param name="oldValue">旧值</param>
+    /// <param name="newValue">新值</param>
+    public VariableValueChangedEventArgs(int variableId, string variableName, string oldValue, string newValue)
+    {
+        VariableId = variableId;
+        VariableName = variableName;
+        OldValue = oldValue;
+        NewValue = newValue;
+        ChangeTime = DateTime.Now;
+    }
+}