Chapter 5. The Application class

This code defines the base Application class:

/* A base application class that keeps track of change functions
   and removes them when the object is destroyed */

if (undefined_p(Application) || !class_p(Application))
{
    class Application
    {
        _ChangeFunctions;
        _TimerIDs;
        _MenuActions;
        _SubMenus;
    static:
        _Instances;
        _MenuItemID = 20000;
        _MenuItems;
        _TraySubmenu;
        _AllMenuActions;
        _TrayMenuPosition = 6;
    }
}

Before defining the class, we test to see if it already exists, using the Gamma predicates undefined_p and class_p functions in an if statement. We want only a single instance of the class so that there is only one copy of the _Instances static variable in the system. This _Instances variable tracks the currently loaded applications, and we do not want several different copies of it floating about.

The instance variable _ChangeFunctions is a list of all the change functions that are defined by the class's .OnChange method. The _TimerIDs, _MenuActions, and _Submenus instance variables are similar lists for any timer IDs, menu actions, and custom submenus that may be defined for the class.