Controller base classes are located in the gui module of the cuba base project and do not contain references to implementation of visual component classes (Swing or Vaadin). This allows you to use them in both types of clients. Instead, base controller classes implement an additional interface
– Window.Wrapper – and delegate execution to the wrapped window.
At the same time concrete controller classes may be contained in gui, web or desktop modules, depending on screen specifics and client client blocks used in the project. If controller is universal and additional functionality is required for different client types it can be implemented in so-called companion classes.
Companion class is located in client module of the corresponding client type (web or desktop) and implements an interface
defined in the controller which uses the companion class. A companion class should be defined in the companions element of the screen XML-descriptor. Controller can retrieve a reference to the companion instance using injection or by
invoking getCompanion(), and then pass control to the companion instance when appropriate, e.g. for extended initialization of visual components
in a way specific to a given client type.
