ScrollViewer.ViewChanged not rise

The ViewChanged should get hit when you try to scroll provided that the ScrollViewer actually contains any scrollable content. You may want to specify an explicit width or height for it depending on your requirements. Please refer to the following example:

<ScrollViewer Height="100" Width="100" ViewChanged="ScrollViewer_ViewChanged" 
                      HorizontalScrollMode="Enabled" HorizontalScrollBarVisibility="Visible">
            <Rectangle Height="500" Width="500" Fill="Green"/>
        </ScrollViewer>