Projektdateien hinzufügen.

WindowsFormsApp1/OP/PropertyObserver.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows.Forms;
+
+namespace WindowsFormsApp1.OP
+{
+    public class PropertyObserver : IObserver<string>
+    {
+        public PropertyObserver()
+        { }
+
+        public void Update(ISubject<string> subject)
+        {
+            MessageBox.Show(subject.GetState());
+        }
+    }
+}