Occurs when a Controller is activated.
This event represents the most useful aspect of Controllers. Handle this event to execute custom code when a Controller is activated, for example, to manage the Controller's Actions visibility and availability. You can also access the current Window and its Action Containers if this Controller is a WindowController class descendant. If it is a ViewController class descendant, you can customize the current View.
A Controller is activated when the Controller.Active collection does not have any elements that have the value set to false left.
For details on how to use Controllers, refer to the Controllers topic.