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;
    }
  });
}