title: Detect, if ScrollBar of ScrollViewer is visible or not
body: <p>I have a TreeView. Now, I want to detect, if the vertical Scrollbar is visible or not.
  When I try it with </p>
  
  <pre><code>var visibility = this.ProjectTree.GetValue(ScrollViewer.VerticalScrollBarVisibilityProperty)
  </code></pre>
  
  <p>(where this.ProjectTree is the TreeView)
  I get always Auto for visibility.</p>
  
  <p>How can I do this to detect, if the ScrollBar is effectiv visible or not?</p>
  
  <p>Thanks.</p>