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Applications developed for the Symbian platform can use a number of different architecture solutions to meet their requirements. One example of a common approach includes the Model - View - Controller (MVC) pattern used in GUI-based applications. In this approach, the application is split into three separate logical parts. Each part contains a different aspect of the entire application, and has a specific role.

In this approach, the model:

• contains and manipulates the data in the application

• is owned by the controller

• is typically implemented in its own class or classes

the view :

• displays the application state known by the model

• receives user input

• notifies the controller of relevant events

• is implemented either with a CCoeControl derived class or a CAknView derived class.

  For more information on these options, see Traditional Symbian UI application architecture and View architecture .

the controller :

• handles application-wide events

• commands the model, typically based on user input

• selects the view to be displayed

• is implemented either with a CAknAppUi -derived class or a CAknViewAppUi derived class.

  For more information on these options, see Traditional Symbian UI application architecture and View architecture .

• requires the implementation of CAknApplication and CAknDocument derived classes.

The pattern is implemented with the following classes.

The CAknApplication -derived class:

• provides the application object expected by the application framework when the application is launched.

• defines the application properties.

• creates the CAknDocument derived class if it does not exist yet.

• if an instance of the application is already running, switches to that instance and exits.

The CAknDocument -derived class:

• creates the controller class

• is the base class for application documents

• Implementing framework requirements