View architecture

The following image illustrates the components of the view architecture approach.

Figure: View architecture classes

Symbian platform applications that follow the view architecture require:

• a UI controller derived from CAknViewAppUi

• a view controller derived from CAknView

• a view or views derived from CCoeControl

The view architecture only allows one view to be active in each application. If a new view is switched to within an application, the current view is immediately deactivated, so this architectural approach is not appropriate in the following cases:

• Applications with any view that cannot cleanly handle unexpected activation of another view in that application.

• Applications that provide views that can be nested over other applications, except where embedding is used.

• Applications that provide controls that can be used inside other applications (for example, using a Web control inside an e-mail viewer to show an e‑mail with HTML content).

Typical responsibilities in this architecture are:

• CAknViewAppUi-derived class acts as a UI controller:

  • It creates one or more CAknView-derived view controllers.

  • It handles events that are not handled by the view controllers.

  • To switch between views, it activates and deactivates views.

  • It handles menu commands passed to it by the view controllers.

  • It receives events such as layout and foreground notifications from the run-time environment.

• CAknView-derived class acts as a view controller

  • It creates one of more CCoeControl-derived views.

  • It handles registering controls for key event handling.

  • It handles menu commands.

• CCoeControl-derived view:

  • Shows application data and state on the screen.

For information on the CAknApplication and CAknDocument-derived classes, see Framework requirements for GUI applications.