Application models

A model class, or usually a set of related classes, encapsulates the purely algorithmic behavior of the application. It presents a well-defined API to other parts of an application. Some of the key relationships are as follows:

• The application's document class constructs and owns the model.

• The App UI contains a pointer/reference to the model.

• An App UI, or an associated class to which it delegates responsibility, receives user commands that the view has passed on and calls model functions appropriately in response to user commands.

• Views also contain a pointer/reference to the model. The views calls model functions appropriately in response to user commands. They can also decide to pass the commands to the App UI.

• Code this is used to draw the screen in a view reads data from the model, but usually does not modify it. Input events handled by a view do, however, cause changes in the model. A straightforward approach is to allow the view to call the model directly. For more complex applications, you may want to provide a separate class that encapsulates handling input events.