Common Widgets class hierarchy

This section describes the Common Widgets class hierarchy and provides an overview of the functionality provided by each class.

A is a user interface component, such as a top-level window (shell), button or list. A graphical user interface is built by creating a tree of widgets. Every widget except the topmost widget in a tree has a parent widget. In the user interface a child widget appears on top of the parent and is normally prevented from drawing outside the bounds of its parent. Each parent widget is responsible for sizing and positioning its children. The parent-child relationship defines the widget tree. The topmost widget in the tree is called a shell widget. Shell widgets are responsible for negotiating with the window manager for their position on the screen, and for the various window decorations that they display, such as a title, border, or close box.

All Common Widgets are subclasses of one of the following classes:

CwPrimitive

A primitive widget has no children.

CwComposite

A composite widget can have zero or more children.

CwShell

A shell widget has exactly one child.

Primitive widgets are the simplest building blocks in Common Widgets. A primitive widget is always the child of another widget. The following table provides brief descriptions of the CwPrimitive class and its subclasses. Classes in italics are abstract classes (they are never instantiated).

Note:

The parent-child relationship is not the same as the class-subclass relationship.

 

Table 28. Primitive hierarchy

Class hierarchy	Responsibility
CwWidget	Defines common behavior for all widgets
CwBasicWidget	Defines common behavior for widgets implemented directly by the platform
CwPrimitive	Defines common behavior for widgets that do not have children
CwArrowButton	Displays an arrow button
CwComboBox	Combines a list and text area to provide a prompted entry field
CwLabel	Displays a static label that can be a string, pixmap, or icon
CwCascadeButton	Used as part of a menu system to trigger submenus
CwDrawnButton	Displays a button drawn by the application
CwPushButton	Displays a push button containing a string, pixmap, or icon
CwToggleButton	Displays a button that has on and off state such as a radio or check button
CwList	Displays a list of strings from which one or more can be selected
CwScrollBar	Displays a vertical or horizontal scroll bar
CwSeparator	Displays a separator line, normally between menu items
CwText	Displays and provides editing capability for text

Composite widgets can have zero or more child widgets. A composite widget's children can include other composite widgets, primitive widgets, or both. Different composite widgets provide various kinds of layout capabilities for arranging children. The following table briefly explains the CwComposite class and its subclasses. Classes in italics are abstract classes.

Table 29. Composite hierarchy

Class hierarchy	Responsibility
CwWidget	Defines common behavior for all widgets
CwBasicWidget	Defines common behavior for widgets implemented directly by the platform
CwComposite	Defines common behavior for widgets that contain child widgets
CwBulletinBoard	Allows application-defined child widget positioning
CwCompositeBox	Defines common behavior for CwMessageBox and CwSelectionBox
CwMessageBox	Provides a notification message, icon, and OK, Cancel, and Help buttons
CwSelectionBox	Provides a list of items to select, a text box showing the selection, and OK, Cancel, Apply, and Help buttons
CwForm	Provides a constraint-based mechanism for laying out child widgets
CwDrawingArea	Performs no child layout and provides an area for performing graphic operations
CwFrame	Provides an optionally labeled frame around its single child widget
CwRowColumn	Provides a mechanism for laying out child widgets in rows or columns
CwScale	Displays a numeric scale with a position indicator
CwScrolledWindow	Allows a child widget to be scrolled using scrollbars
CwMainWindow	Provides layout management for a menu bar and optionally scrollable work area

Shell widgets provide the protocol between the application interface and the window manager. The following table provides brief descriptions of the CwShell class and its subclasses. Classes in italics are abstract classes.

Table 30. Shell hierarchy

Class hierarchy	Responsibility
CwWidget	Defines common behavior for all widgets
CwBasicWidget	Defines common behavior for widgets implemented directly by the platform
CwShell	Defines common behavior for the top-level widgets of windows and dialogs
CwOverrideShell	A pop-up window that bypasses window management, and normally appears on top of all other widgets
CwWMShell	Defines common behavior for shell widgets that do not bypass window management
CwTopLevelShell	Provides a normal window with standard appearance and decorations
CwTransientShell	A pop-up dialog window that does not bypass window management
CwDialogShell	A pop-up window used to implement modal and modeless dialog windows