viewmodel ins wpf gepackt, build failed

DaSaSo.Wpf/ViewModel/ObservableObject.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace DaSaSo.Wpf.ViewModel
+{
+    public class ObservableObject : INotifyPropertyChanged
+    {
+        public event PropertyChangedEventHandler? PropertyChanged;
+        protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null)
+        {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+    }
+}