Apply fix to sample to show proper way to use TokenizingTextBox Binding to ItemsSource

Avoids bug #4248

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/TokenizingTextBox/TokenizingTextBoxPage.xaml.cs

@@ -90,7 +90,9 @@ namespace Microsoft.Toolkit.Uwp.SampleApp.SamplePages
         private AdvancedCollectionView _acv;
         private AdvancedCollectionView _acvEmail;
 
-        private ObservableCollection<SampleEmailDataType> _selectedEmails;
+        public ObservableCollection<SampleDataType> SelectedTokens { get; set; }
+
+        public ObservableCollection<SampleEmailDataType> SelectedEmails { get; set; }
 
         public TokenizingTextBoxPage()
         {
@@ -112,7 +114,10 @@ namespace Microsoft.Toolkit.Uwp.SampleApp.SamplePages
 
         public void OnXamlRendered(FrameworkElement control)
         {
-            _selectedEmails = new ObservableCollection<SampleEmailDataType>();
+            SelectedTokens = new();
+            SelectedEmails = new();
+
+            control.DataContext = this;
 
             if (_ttb != null)
             {
@@ -150,7 +155,6 @@ namespace Microsoft.Toolkit.Uwp.SampleApp.SamplePages
             {
                 _ttbEmail = ttbEmail;
 
-                _ttbEmail.ItemsSource = _selectedEmails;
                 _ttbEmail.ItemClick += EmailTokenItemClick;
                 _ttbEmail.TokenItemAdding += EmailTokenItemAdding;
                 _ttbEmail.TokenItemAdded += EmailTokenItemAdded;

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/TokenizingTextBox/TokenizingTextBoxXaml.bind

@@ -37,6 +37,7 @@
       </TextBlock>
       <controls:TokenizingTextBox
           x:Name="TokenBox"
+          ItemsSource="{Binding SelectedTokens}"
           PlaceholderText="Add Actions"
           QueryIcon="{ui:SymbolIconSource Symbol=Setting}"
           MaxHeight="104"
@@ -65,7 +66,7 @@
         <Run>Current Edit: </Run>
         <Run Text="{Binding Text, ElementName=TokenBox}"/>
       </TextBlock>
-      <ItemsControl ItemsSource="{Binding ItemsSource, ElementName=TokenBox}"/>
+      <ItemsControl ItemsSource="{Binding SelectedTokens}"/>
     </StackPanel>
 
     <StackPanel Grid.Row="1">
@@ -73,6 +74,7 @@
                  Margin="0,0,0,4"/>
       <controls:TokenizingTextBox
             x:Name="TokenBoxEmail"
+            ItemsSource="{Binding SelectedEmails}"
             PlaceholderText="Select Names"
             MaxHeight="104"
             HorizontalAlignment="Stretch"