virtual - Virtual control

Virtual controls define a widget (tab) stack in order to display different forms for different types. Depending on the data type of the instance currently selected in the data source, the control tries to locate a field control in the corresponding GUI class or in the inheritance hierarchy. When being found, the field control will be loaded to a tab stack entry (when not yet existing) and the tab stack entry will be activated.

When the data source for the field control is user-defined, or when for some other reason any data type might be displayed for the field control, the field control should get an empty implementation in the VOID GUI class. When being used for displaying weak-typed collections, it is sufficient to implement the field control in the lowest base class.