private static void OnDurationChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            SmoothScrollViewer viewer = sender as SmoothScrollViewer;

            viewer.m_animation.Duration        = new Duration((TimeSpan)e.NewValue);
            viewer.m_endingAnimation.BeginTime = viewer.m_animation.Duration.TimeSpan;
        }
        private static void OnOffsetChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            SmoothScrollViewer viewer = sender as SmoothScrollViewer;

            viewer.ScrollToVerticalOffset((double)e.NewValue);
        }