5.2 The class hierarchy for DUIM-Sheets
5.2.1 The base classes in the DUIM-Sheets library
The base classes for the majority of subclasses exposed from the DUIM-Sheets library are <sheet> and <event>, although a number of additional subclasses of <object> are also exposed.
The base classes exposed by the DUIM-Sheets library are shown in Table 5.1. Only <sheet>, and <event> have any subclasses defined. An <event> is an object representing some sort of event. See Section 5.2.2 on page 203 for details of the subclasses of <event>.
<object> | ||
<sheet> | ||
<display> | ||
<port> | ||
<clipboard> | ||
<caret> | ||
<pointer> | ||
<medium· | ||
<frame-manager· | ||
<event> |
<sheet>As already mentioned, a sheet is the basic unit of window applications, and they can be nested in a parent-child hierarchy. A subclass of sheet is provided --
<display>-- which is an object that represents a single display (or screen) on a display server. All sheets can be attached to a display.<port>A port is a connection to a display server. A display, together with all the sheets attached to it, is associated with a port, which manages a primary input device, such as a keyboard, a pointing device, such as a mouse, and an event processor that dispatches events to the appropriate sheet.
<clipboard>This class is used as a clipboard that can be used to hold information temporarily while it is transferred from one sheet to another, or between applications. Clipboards provide support for the standard Cut, Copy, and Paste commands common in most applications.
<caret>and<pointer>- These two classes form an interface between the keyboard and the display, and the pointing device and the display, respectively.
- The
<caret>represents the position on screen that characters typed on the keyboard will be placed. This is often a position in a document. - The
<pointer>represents the position of the pointing device on the screen, and thus shows the area that will be affected by any events generated with the pointing device, such as pressing or clicking one of the buttons on the device. <pointer-drag-event>- The class of events where the pointer for the pointing device attached to the computer is moving, and one of the buttons on the pointing device is pressed down as well. The effects of this event are rather like a combination of the
<button-press-event>and<pointer-motion-event>classes. For more information about these and other pointer event classes, see Section 5.2.3 on page 205. <pointer-enter-event>- This event is used to describe the event where the pointer for the pointing device enters a specified area of the screen, such as a sheet. For more information about these and other pointer event classes, see Section 5.2.3 on page 205.
<medium>A medium represents a destination for drawn or written output. It has several items associated with it, such as a drawing plane, foreground and background colors, and default line and text styles.
<frame-manager>- A frame manager represents the "look and feel" of a frame. This controls standard interface elements for the platform you are delivering on, such as the appearance and behavior of title bars, borders, menu commands and scroll bars. Unless you are developing for more than one platform, you do not need to be too concerned with frame managers, since you will only using the default frame manager.