Core Windowing Classes

The fundamental graphical element in MrEd's windowing toolbox is an area. The following classes implement the different types of areas in the windowing toolbox:

• Containers -- areas that can contain other areas:
  • frame% -- a frame is a top-level window that the user can move and resize.
  • dialog% -- a dialog is a modal top-level window; when a dialog is shown, other top-level windows are disabled until the dialog is dismissed.
  • panel% -- a panel is a subcontainer within a container. The toolbox provides two subclasses of panel%: vertical-panel% and horizontal-panel%.
  • pane% -- a pane is a lightweight panel. It has no graphical representation or event-handling capabilities. The pane% class has three subclasses: vertical-pane%, horizontal-pane%, and grow-box-spacer-pane%.

• Containees -- areas that must be contained within other areas:
  • panel% -- a panel is a containee as well as a container.
  • pane% -- a pane is a containee as well as a container.
  • canvas% -- a canvas is a subwindow for drawing on the screen.
  • editor-canvas% -- an editor canvas is a subwindow for displaying a text editor or pasteboard editor. The editor-canvas% class is documented with the editor classes in Editor Toolbox.
  • Controls -- containees that the user can manipulate:
    • message% -- a message is a static text field or bitmap with no user interaction.
    • button% -- a button is a clickable control.
    • check-box% -- a check box is a clickable control; the user clicks the control to set or remove its check mark.
    • radio-box% -- a radio box is a collection of mutually exclusive radio buttons; when the user clicks a radio button, it is selected and the radio box's previously selected radio button is deselected.
    • choice% -- a choice item is a pop-up menu of text choices; the user selects one item in the control.
    • list-box% -- a list box is a scrollable lists of text choices; the user selects one or more items in the list (depending on the style of the list box).
    • text-field% -- a text field is a box for simple text entry.
    • slider% -- a slider is a dragable control that selects an integer value within a fixed range.
    • gauge% -- a gauge is a output-only control (the user cannot change the value) for reporting an integer value within a fixed range.

As suggested by the above listing, certain areas, called containers, manage certain other areas, called containees. Some areas, such as panels, are both containers and containees.

Most areas are windows, but some are non-windows. A window, such as a panel, has a graphical representation, receives keyboard and mouse events, and can be disabled or hidden. In contrast, a non-window, such as a pane, is useful only for geomerty management; a non-window does not receive mouse events, and it cannot be disabled or hidden.

Every area is an instance of the area<%> interface. Each container is also an instance of the area-container<%> interface, whereas each containee is an instance of subarea<%>. Windows are instances of window<%>. The area-container<%>, subarea<%>, and window<%> interfaces are subinterfaces of area<%>. Figure 2.1 shows more of the type hierarchy under area<%>.

                           area<%>
       ______________________|_______________
       |                  |                 |
  subarea<%>          window<%>      area-container<%>      
       |____       _______|__________       |
            |      |                |       |
           subwindow<%>          area-container-window<%>
        ________|________                |
        |               |                |
     control<%>       canvas<%>   top-level-window<%>

-- Figure: Core area type hierarchy --

Figure 2.2 extends the previous figure to show the complete type hierarchy under area<%>. To avoid intersecting lines, the hierarchy is drawn for a cylindrical surface; lines from subarea<%> and subwindow<%> wrap from the left edge of the diagram to the right edge.

                           area<%>
        _____________________|_______________
        |               |                   |
      subarea<%>     window<%>       area-container<%>      
<<<____|____       _____|__________       __|___  ___________________<<<
            |      |              |       |    |  |                  
           subwindow<%>           |       |    |  |                  
<<<______________|___________     |       |    |  |                 _<<<
            |               |     |       |    pane%                |
       control<%>           |     |       |     |- horizontal-pane% |
        |- message%         |     |       |     |- vertical-pane%   |
        |- button%          |     |       |                         |
        |- check-box%       |  area-container-window<%>             |
        |- slider%          |        |                              |
        |- gauge%           |        |            __________________|
        |- text-field%      |        |            |   
        |- radio-box%       |        |-------- panel%       
        |- list-control<%>  |        |          |- horizontal-panel%
            |- choice%      |        |          |- vertical-panel%
            |- list-box%    |        |          
                            |        |- top-level-window<%>
                            |           |- frame% 
                            |           |- dialog%
                         canvas<%>
                          |- canvas%
                          |- editor-canvas%

-- Figure: Complete area type hierarchy (drawn on a cylinder with wraparound lines) --

Menu bars, menus, and menu items are graphical elements, but not areas (i.e., they do not have all of the properties that are common to areas, such as an adjustable graphical size). Instead, the menu classes form a separate container-containee hierarchy:

• Menu Item Containers
  • menu-bar% -- a menu bar is a top-level collection of menus that are associated with a frame.
  • menu% -- a menu contains a set of menu items. The menu can appear in a menu bar, in a popup menu, or as a submenu in another menu.
  • popup-menu% -- a popup menu is a top-level menu that is dynamically displayed in a canvas or editor canvas.

• Menu Items
  • separator-menu-item% -- a separator is an unselectable line in a menu or popup menu.
  • menu-item% -- a menu item is a selectable text item in a menu. When the item is selected, its callback procedure is invoked.
  • checkable-menu-item% -- a checkable menu item is a text item in a menu; the user selects a checkable menu item to toggle a check mark next to the item.
  • menu% -- a menu is a menu item as well as a menu item container.

menu-item<%>                menu-item-container<%>
    |                              |
    |- separator-menu-item%   _____|___
    |- labelled-menu-item<%>  |       |- menu-bar%
        _________|_________   |       |- popup-menu%
        |                 |   | 
        |                 menu%
        |
        |- selectable-menu-item<%>
            |- menu-item%
            |- checkable-menu-item%

-- Figure: Menu type hierarchy --