9.2 The class hierarchy for DUIM-Frames
9.2.1 The <frame> class and its subclasses
The base class for all DUIM frames is the <frame> class, which is itself a subclass of <object>. In addition, there are a number of classes related to commands that are subclasses of <object>, together with a number of classes related to events that occur in frames. Table 9.1 shows the overall class hierarchy for the base classes exported by the DUIM-Frames library.
<object> | |||
<gadget> | |||
<page> | See Section 9.2.4 | ||
<frame> | See Section 9.2.2 | ||
<event> | |||
<frame-event> | See Section 9.2.3 | ||
<simple-command> | |||
<simple-undoable-command> | |||
<command-table> | |||
<command-table-menu-item> | |||
The <frame> class represents the base class for all types of frame. An introduction to the subclasses available is given in Section 9.2.2.
The <event> class represents the base class for all events that can occur. Although this class and the <frame-event> subclass are exposed by the DUIM-Sheets library, the subclasses of <frame-event> itself are exposed by the DUIM-Frames library. See Section 9.2.3 on page 704 for an introduction to these subclasses. See Chapter 5, "DUIM-Sheets Library", for a complete description of the DUIM-Sheets library.
The remaining four classes exposed by the DUIM-Frames library relate to commands and their use in application menus.
<simple-command>- This class is used to create the most basic type of command. A command is an operation that can be invoked as a callback from a menu item, a button, or other suitable interface control.
<simple-undoable-command>- This class is used to define commands whose effects can be reversed. Typically, the user chooses the command Edit > Undo to reverse the effects of a command of this class.
<command-table>- The
<command-table>class is used to define the complete menu structure of an application frame, from the menu bar and menus to the menu items on each menu. <command-table-menu-item>- This class represents a menu item on a menu defined in a command table.