title: ScrollViewer's Viewport Height VS Actual Height
body: <p>Both are quite general terms but I'm curious to know when these height will be different apart from the case we're using Virtualization?</p>
  
  <p>One more question:
  I read on MSDN:</p>
  
  <p><em>If CanContentScroll is true, the values of the ExtentHeight, ScrollableHeight, ViewportHeight, and VerticalOffset properties are number of items. If CanContentScroll is false, the values of these properties are Device Independent Pixels.</em></p>
  
  <p>However I'm facing an issue with ViewPort Height: I've 2 listbox in application:<br>
   1. Which have Virtualization Enabled and CanContentScroll = True.<br>
   2. Which have no virtualization and CanContentScroll = True.  </p>
  
  <p>In ListBox 1 while drag-drop Viewport Height comes to 4/5 (Number of elements currently visible). However in ListBox 2 i get Viewport Height equal to Actual Height of Listbox.  </p>
  
  <p>Why this difference?</p>
  
  <p>Few more findings:<br>
  <em>1. Scrollable Height is number of items not visible in scrollviewer<br>
  2. Viewport Height is number of items visible in scrollviewer.<br>
  Thus Viewport Height + ScrollableHeight = Extent Height</em></p>
  
  <p><em>Can someone please explain what's the difference between two listboxes? I need ViewPort hieght in case of Listbox 1</em></p>