public MapFrame ActivatedMapFrame {get;}

{
  //Deactivate any activated map frame
  //Note: we are on the UI thread!
  layoutView.DeactivateMapFrame();//no-op if nothing activated

  //or - check if a  map frame is activated first...
  if (layoutView.ActivatedMapFrame != null)
    //Note: we are on the UI thread!
    layoutView.DeactivateMapFrame();
}

{
  //The active view must be a layout view.
  var lv = LayoutView.Active;
  if (lv == null)
    return;

  var map_view = lv.ActivatedMapView;
  if (map_view != null)
  {
    //TODO - use activated map view
  }
  var map_frame = lv.ActivatedMapFrame;
  if (map_frame != null)
  {
    //TODO - use activated map frame
  }
}