The view that is going to become active. 
   Namespace:   Autodesk.Revit.UI.Events  
  Assembly:   RevitAPIUI  (in RevitAPIUI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2010 
  Namespace:   Autodesk.Revit.UI.Events  
  Assembly:   RevitAPIUI  (in RevitAPIUI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2010