Re: Properties

[Shark8 <onewingedshark@gmail.com>]

On Dec 1, 8:59 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
>The main problem is the interface of such a library. There are
>multiple parallel hierarchies need to be handled: a hierarchy
>of widget types, a hierarchy of widget containers, a hierarchy
>of event handlers (events are filtered, propagated, swallowed,
>re-generated).
>
> --
> Regards,
> Dmitry A. Kazakovhttp://www.dmitry-kazakov.de

Why not have an INTERFACE hierarchy in addition to the GUI_Object
hierarchy? This would allow for an easy way for foreign-language
objects to be incorporated, to some extent, into applications which
use this hypothetical library.... with only the added encumberment of
forcing more up-front design. (Usu. a good thing.)

Additionally, it could help with keeping the GUI_Object hierarchy
smaller as there are many GUI items which are themselves composed of
other GUI items. A scroll-bar, for example, has two distinct
interfaces: the Button[s] and the slider-bar.

The event-handler hierarchy seems to be the most 'interesting', not
because of the events themselves, but because of the problem of how
best to hook them; as you said they can be consumed, passed-through,
emitted, and so-forth. They should, therefore be lightweight (as we
don't want to transmit unnecessary information), quick in construction
(this will impact the GUIs responsiveness) and clean in destruction
(no memory leaks, please).

By "widget containers" do you mean something like
Ada.Containers.Vectors initialized to the classwide-type of the root
of the GUI_Object hierarchy, OR do you mean some component which
contains other components (like a panel, perhaps)? {I'm inclined to
believe you meant the latter.}

Finally, I've been quite impressed with Delphi's Visual Component
Library (VCL). Microsoft's MFC and Java's JFC seem to have been
'inspired' [or copied] from the VCL, but neither presents itself as
uniform & usable/mature [if you will] as the VCL. While the VCL
doesn't use interfaces it does make nice use of properties; event
handlers are get/set w/ properties and handlers are not required to be
installed for every object like they are in Java; I believe that
internally Delphi uses something like this:
If Assigned(Handler) Then Handler^(Sender); {Assigned tests for null.}