Can I ask what is the goal of detecting if ScrollBar is pressed? If you need to know when it is scrolling or being dragged there are events you can attach to in the ScrollViewer:
scrollViewer.AddHandler(ScrollBar.ScrollEvent, ...);
scrollViewer.AddHandler(Thumb.DragStartedEvent, ...);
scrollViewer.AddHandler(Thumb.DragDeltaEvent, ...);
scrollViewer.AddHandler(Thumb.DragCompletedEvent, ...);
About finding the bar, if you are using our NoesisTheme, the
ScrollViewer template contains horizontal and vertical scroll bars named respectively as
PART_HorizontalScrollBar and
PART_VerticalScrollBar. Calling the following code should get you the vertical scroll bar:
ScrollBar sb = (ScrollBar)scrollviewer.Template.FindName("PART_VerticalScrollBar", scrollviewer);
Isn't that working for you? Are you using your own template for the ScrollViewer?