public enum LayoutViewEventHint : System.Enum, System.IComparable, System.IConvertible, System.IFormattable, System.ISpanFormattable  

//Report the event args when a the layout view has changed.

//At 2.x - ArcGIS.Desktop.Layouts.Events.ActiveLayoutViewChangedEvent.Subscribe((args) =>
//{
//  System.Windows.MessageBox.Show("ActiveLayoutViewChangedEvent:" +
//    Environment.NewLine +
//    "   arg Layoutview: " + args.LayoutView.Layout.Name +
//    Environment.NewLine +
//    "   arg Type: " + args.Type.ToString());
//});

ArcGIS.Desktop.Layouts.Events.LayoutViewEvent.Subscribe((args) =>
{
  //this is the view being activated 
  var layout = args.LayoutView?.Layout?.Name ?? "null";

  if (args.Hint == LayoutViewEventHint.Activated)
  {
    System.Diagnostics.Debug.WriteLine($"LayoutViewEventHint.Activated: {layout}");
  }
  else if (args.Hint == LayoutViewEventHint.Deactivated)
  {
    System.Diagnostics.Debug.WriteLine($"LayoutViewEventHint.Deactivated: {layout}");
  }
});

//Report the event args when a layout is closed.

//At 2.x - ArcGIS.Desktop.Layouts.Events.LayoutClosedEvent.Subscribe((args) =>
//{
//  System.Windows.MessageBox.Show("LayoutClosedEvent:" +
//  Environment.NewLine +
//  "   arg LayoutPane: " + args.LayoutPane.Caption);
//});

ArcGIS.Desktop.Layouts.Events.LayoutViewEvent.Subscribe((args) =>
{
  var lv = args.LayoutView;
  var layoutName = lv?.Layout?.Name ?? "null";
  if (args.Hint == LayoutViewEventHint.Closed)
  {
    System.Diagnostics.Debug.WriteLine($"LayoutViewEventHint.Closed: {layoutName}");
  }
});

//Report the event args when a layout is closing.

//At 2.x - ArcGIS.Desktop.Layouts.Events.LayoutClosingEvent.Subscribe((args) =>
//{
//  System.Windows.MessageBox.Show("LayoutClosingEvent:" +
//  Environment.NewLine +
//  "   arg Layout: " + args.Layout.Name +
//  Environment.NewLine +
//  "   arg LayoutPane: " + args.LayoutPane.Caption);
//});

ArcGIS.Desktop.Layouts.Events.LayoutViewEvent.Subscribe((args) =>
{
  var lv = args.LayoutView;
  var layoutName = lv?.Layout?.Name ?? "null";
  if (args.Hint == LayoutViewEventHint.Closing)
  {
    System.Diagnostics.Debug.WriteLine($"LayoutViewEventHint.Closing: {layoutName}");
  }
});

//Report the event args when a layout's paused state is changed.

//At 2.x - ArcGIS.Desktop.Layouts.Events.LayoutPauseDrawingChangedEvent.Subscribe((args) =>
//{
//  System.Windows.MessageBox.Show("LayoutPauseDrawingChangedEvent:" +
//    Environment.NewLine +
//    "   arg Layoutview: " + args.LayoutView.Layout.Name +
//    Environment.NewLine +
//    "   arg Type: " + args.Paused.ToString());
//});

//At 3.x use LayoutViewEvent
ArcGIS.Desktop.Layouts.Events.LayoutViewEvent.Subscribe((args) =>
{
  var lv = args.LayoutView;
  var layout = args.LayoutView?.Layout;

  switch (args.Hint)
  {
    case LayoutViewEventHint.PauseDrawingChanged:
      System.Diagnostics.Debug.WriteLine($"LayoutViewEvent ElementEventHint: {args.Hint.ToString()}");
      break;
  }
});

//Report the event args for the different types of layout view events.

ArcGIS.Desktop.Layouts.Events.LayoutViewEvent.Subscribe((args) =>
{
  var lv = args.LayoutView;
  var layout = args.LayoutView?.Layout;

  switch(args.Hint)
  {
    case LayoutViewEventHint.PauseDrawingChanged:
    case LayoutViewEventHint.DrawingComplete:
    case LayoutViewEventHint.ExtentChanged:
    case LayoutViewEventHint.Activated:
    case LayoutViewEventHint.Deactivated:
    case LayoutViewEventHint.Closed:
    case LayoutViewEventHint.Closing:
    case LayoutViewEventHint.Opened:
      System.Diagnostics.Debug.WriteLine($"LayoutViewEvent ElementEventHint: {args.Hint.ToString()}");
      break;
  }
});