Chapter 1

Now it's time to be precise about how windows and controls work together to enable your
application to share the screen with other applications and to enable the different parts of
your application to work together.
Symbian OS is a full multitasking system in which multiple applications may run
concurrently. The screen is a single resource that must be shared among all these
applications. Symbian OS implements this sharing using the window server. Each
application draws to one or more windows; the window server manages the windows,
ensuring that the correct window or windows are displayed, exposing and hiding windows as
necessary, and managing overlaps (Figure 11.8).
Figure 11.8
An application must also share the screen effectively between its own components. These
components include the main application view, the button bar, and other ornaments: dialogs,
menus, and the like. An application uses controls for its components. Some controls –
dialogs, for instance – use an entire window, but many others simply reside alongside other
controls on an existing window. The buttons on a button bar behave this way, as do the fleet
views in the main application view of Battleships.
11.5.1 CONE
Every GUI client uses CONE, the control environment, to provide the basic framework for
controls and for communication with the window server in Figure 11.9: