ABAP_to_the_Future

12
Web Dynpro ABAP and Floorplan Manager
12.1.3 Controller
A controller is any sort of computer program that knows about one or more models
and one or more views; it’s a sort of broker that handles communication
between them. Inside a controller, you need to code business logic to decide if a
certain view should be used to display the data of a certain model. When a view
sends back a message saying the user has done something, you need to add code
to the controller so that it can decide if the model needs to know this, or if the
controller can deal with the input itself (e.g., an instruction to display exactly the
same data in a different format can be handled by the controller simply calling up
another view without having to bother the model). The controller must be careful
never to let the view and the model know of each other’s existence (otherwise the
entire universe will explode—or something almost as terrible).
The controller concept in WDA is even more complicated than you might expect,
because there isn’t only one controller but a number of them. The thing to
remember is that out of all the myriad controllers you may see, the component
controller is the head honcho, numero uno,the leader of the pack, the king of the
hill, and the undisputable top cat.
The controllers in WDA are generated automatically: the component controller at
the start and other controllers as and when the windows and views are created. It
is also possible to create additional controllers manually.
What is the “component” that is being controlled? A component can be thought
of as the equivalent of the module pool program (it isn’t really, but it’s close
enough). If you treat the two terms as interchangeable, then the component controller
becomes the program controller, an d the waters are slightly less muddy.
The component controller can be accessed by all the views and can talk back to
them, as might be expected; any other controllers knocking around are just willing
accomplices.
There are “view controllers” and “window controllers,” but they are not controllers
in any meaningful sense of the wo rd, because such controllers are one with
their respective windows and views and never talk to the model like proper controllers
do.
Thus, as mentioned earlier, just because something is called a controller, walks
like a controller, and quacks like a controller, you shouldn’t treat it like a controller
if it isn’t one; make sure all contro ller-type tasks are delegated to a real controller.
514