void viewClosed(int idNum)
This method must be exposed by tools and managers. It is called whenever a view is closed (either by the user or by another client). The argument idNum is the unique identifier for the newly view that just closed.
Clients that associate themselves with a single view at start-up, e.g. the active view, may want to shut down (or become inactive) if that view should close. Clients that operate on all views may want to shut down (or become inactive) if the last remaining view closes. This method provides the means to do so. This method may do nothing, but it must always be exposed.