Projektdateien hinzufügen.

WindowsFormsApp1/OP/IObserver.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace WindowsFormsApp1.OP
+{
+    public interface IObserver<T>
+    {
+        /// <summary>
+        /// Receive update from subject
+        /// </summary>
+        void Update(ISubject<T> subject);
+    }
+}