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/VariableValueChangedEventArgs.cs

@@ -0,0 +1,50 @@
+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;
+    }
+}