update doc

src/Shared/HandyControlDemo_Shared/UserControl/Basic/ChatBox.xaml

@@ -17,7 +17,7 @@
             <RowDefinition/>
             <RowDefinition Height="Auto"/>
         </Grid.RowDefinitions>
-        <ListBox Name="ListBoxChat" ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.CanContentScroll="False" Background="Transparent" hc:ChatBubble.MaxWidth="300" BorderThickness="0" Style="{StaticResource StackPanelVerticalListBox}" ItemsSource="{Binding ChatInfos}">
+        <ListBox Name="ListBoxChat" ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.CanContentScroll="False" Background="Transparent" BorderThickness="0" Style="{StaticResource StackPanelVerticalListBox}" ItemsSource="{Binding ChatInfos}">
             <hc:Interaction.Triggers>
                 <hc:RoutedEventTrigger RoutedEvent="hc:ChatBubble.Selected">
                     <hc:EventToCommand Command="{Binding ReadMessageCmd}" PassEventArgsToCommand="True" />
@@ -25,7 +25,7 @@
             </hc:Interaction.Triggers>
             <ListBox.ItemTemplate>
                 <DataTemplate>
-                    <hc:ChatBubble Role="{Binding Role}" Type="{Binding Type}" Content="{Binding Message}" Tag="{Binding}"/>
+                    <hc:ChatBubble MaxWidth="300" Role="{Binding Role}" Type="{Binding Type}" Content="{Binding Message}" Tag="{Binding}"/>
                 </DataTemplate>
             </ListBox.ItemTemplate>
         </ListBox>

src/Shared/HandyControlDemo_Shared/UserControl/Basic/ChatBox.xaml.cs

@@ -10,17 +10,12 @@ namespace HandyControlDemo.UserControl
         public ChatBox()
         {
             InitializeComponent();
-
             ListBoxChat.ItemContainerGenerator.ItemsChanged += ItemContainerGenerator_ItemsChanged;
         }
 
         private void ItemContainerGenerator_ItemsChanged(object sender, System.Windows.Controls.Primitives.ItemsChangedEventArgs e)
         {
-            if (_scrollViewer == null)
-            {
-                _scrollViewer = VisualHelper.GetChild<ScrollViewer>(ListBoxChat);
-            }
-
+            _scrollViewer ??= VisualHelper.GetChild<ScrollViewer>(ListBoxChat);
             _scrollViewer?.ScrollToBottom();
         }
     }