Divided the code into functional modules

Services/INotificationService.cs

@@ -0,0 +1,36 @@
+namespace HeartRateMonitorAndroid.Services
+{
+    /// <summary>
+    /// 通知服务接口
+    /// </summary>
+    public interface INotificationService
+    {
+        /// <summary>
+        /// 初始化通知服务
+        /// </summary>
+        void Initialize();
+
+        /// <summary>
+        /// 显示心率通知
+        /// </summary>
+        /// <param name="currentHeartRate">当前心率</param>
+        /// <param name="avgHeartRate">平均心率</param>
+        /// <param name="minHeartRate">最低心率</param>
+        /// <param name="maxHeartRate">最高心率</param>
+        /// <param name="duration">监测时长</param>
+        void ShowHeartRateNotification(int currentHeartRate, double avgHeartRate, int minHeartRate, int maxHeartRate, TimeSpan duration);
+
+        /// <summary>
+        /// 取消通知
+        /// </summary>
+        void CancelNotification();
+
+        /// <summary>
+        /// 显示重连通知
+        /// </summary>
+        /// <param name="title">标题</param>
+        /// <param name="message">消息内容</param>
+        /// <param name="attemptCount">尝试次数</param>
+        void ShowReconnectionNotification(string title, string message, int attemptCount);
+    }
+}