Update version

samples/NotificationFlyoutSample/ObservableObject.cs

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+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+
+namespace NotificationFlyoutSample
+{
+    public class ObservableObject : INotifyPropertyChanged
+    {
+        public event PropertyChangedEventHandler PropertyChanged;
+
+        public virtual void OnPropertyChanged([CallerMemberName] string propertyName = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+
+        protected virtual bool SetProperty<T>(ref T backingStore, T value, [CallerMemberName] string propertyName = "",
+            Action onChanged = null, Func<T, T, bool> validateValue = null)
+        {
+            if (EqualityComparer<T>.Default.Equals(backingStore, value))
+                return false;
+
+            if (validateValue != null && !validateValue(backingStore, value))
+                return false;
+
+            backingStore = value;
+            onChanged?.Invoke();
+            OnPropertyChanged(propertyName);
+            return true;
+        }
+    }
+}