protected internal virtual void OnShow( 
   bool isVisible
)

private SubscriptionToken _eventToken = null;
// Called when the visibility of the DockPane changes.
protected override void OnShow(bool isVisible)
{
  if (isVisible && _eventToken == null) //Subscribe to event when dockpane is visible
  {
    _eventToken = MapSelectionChangedEvent.Subscribe(OnMapSelectionChangedEvent);
  }

  if (!isVisible && _eventToken != null) //Unsubscribe as the dockpane closes.
  {
    MapSelectionChangedEvent.Unsubscribe(_eventToken);
    _eventToken = null;
  }
}
//Event handler when the MapSelection event is triggered.
private void OnMapSelectionChangedEvent(MapSelectionChangedEventArgs obj)
{
  MessageBox.Show("Selection has changed");
}