GEOS SDK TechDocs
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2.4 Device Drivers
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3 Object-Oriented Programming
The GEOS User Interface (UI) is a special entity. While it consists primarily of dynamic libraries, it can be thought of as a user interface driver.
Applications define their UI needs in a high-level language (called Goc and developed by Geoworks) interpreted by a special C preprocessor. Applications in general do not have to manifest windows, scrollbars, buttons, menus, or dialog boxes; instead, they use generic objects from the provided UI object library. These generic objects have no inherent visual representation; instead, they have a strictly-defined functionality and API.
A Specific User Interface library, at run-time, determines the visual representation each object takes depending on its context. For example, a GenInteraction generic object may appear as a menu, a dialog box, or a merely a grouping of other generic UI gadgets. Additionally, a menu GenInteraction may be represented as a vertical menu in one Specific UI but as a horizontal bar of choices in another.
Although such a system may appear to take some control of the application's user interface away from the programmer, in actuality quite the opposite is true. The use of a generic UI frees the programmer to concentrate on other issues and features without worrying about whether the application conforms to one or more specifications. The programmer does not have to worry about window positioning or clipping areas (unless he or she wants to), and menus and dialog boxes are almost entirely automatic.
Additionally, the programmer can set
hints
for individual generic objects; hints can help the specific UI decide how the object should appear or be arranged on the screen. Not all hints are allowed in all specific UIs, so a particular specific UI may ignore certain hints while implementing others. For example, a dialog box that has three buttons within it may have the hint
HINT_ORIENT_CHILDREN_VERTICALLY
to indicate the buttons should appear in a column rather than a row.
GEOS SDK TechDocs
|
| 2.4 Device Drivers
| 3 Object-Oriented Programming