修复S7服务轮询问题

DMS.Core/Events/VariableValueChangedEventArgs.cs

@@ -0,0 +1,45 @@
+namespace DMS.Core.Events
+{
+    /// <summary>
+    /// 变量值变更事件参数
+    /// </summary>
+    public class VariableValueChangedEventArgs : EventArgs
+    {
+        /// <summary>
+        /// 变量ID
+        /// </summary>
+        public int VariableId { get; set; }
+
+        /// <summary>
+        /// 变量名称
+        /// </summary>
+        public string VariableName { get; set; }
+
+        /// <summary>
+        /// 旧值
+        /// </summary>
+        public string OldValue { get; set; }
+
+        /// <summary>
+        /// 新值
+        /// </summary>
+        public string NewValue { get; set; }
+
+        /// <summary>
+        /// 更新时间
+        /// </summary>
+        public DateTime UpdateTime { get; set; }
+
+        /// <summary>
+        /// 构造函数
+        /// </summary>
+        public VariableValueChangedEventArgs(int variableId, string variableName, string oldValue, string newValue, DateTime updateTime)
+        {
+            VariableId = variableId;
+            VariableName = variableName;
+            OldValue = oldValue;
+            NewValue = newValue;
+            UpdateTime = updateTime;
+        }
+    }
+}