public sealed class PresentationViewEvent : ArcGIS.Core.Events.CompositePresentationEvent<PresentationViewEventArgs> 

//For UI context changes associated with a presentation, subscribe to the PresentationView
//event - views activated/deactivated, views opened/closed
ArcGIS.Desktop.Presentations.Events.PresentationViewEvent.Subscribe((args) =>
{
  //get the affected view and presentation
  var view = args.PresentationView;
  var presentation = args.PresentationView?.Presentation;
  if (presentation == null)
  {
    //FYI presentationview and/or presentation can be null...
    //eg closed, deactivation
  }
  //Check what triggered the event and take appropriate action
  switch (args.Hint)
  {
    case PresentationViewEventHint.Activated:
      // Presentation view activated
      break;
    case PresentationViewEventHint.Opened:
      //A PresentationView has been initialized and opened
      break;
    case PresentationViewEventHint.Deactivated:
      // Presentation view deactivated
      break;
    case PresentationViewEventHint.Closing:
      //Set args.Cancel = true to prevent closing
      break;
    case PresentationViewEventHint.ExtentChanged:
      //presentation view extent has changed
      break;
    case PresentationViewEventHint.DrawingComplete:
      break;
    case PresentationViewEventHint.PauseDrawingChanged:
      break;
  }
});