OOP: Subclassing and passing class reference via window property 2004-07-29 -- Jens Weiermann Newsgroups: sv.clarion.suggestions
Jonathan Kay wrote:
> Currently writing a generic class for subclassing is painful; you have to
> maintain the address of the class in a QUEUE so you can call virtual methods
> from within the sub-classed procedure. And since this has to be module level
> data you've got to synchronize it too.
I've found a way to make this easier. I'm storing the address of my Clarion
class instance in a window property of the sublclassed window (via the
SetProp api). This way, I can reference assign that address to a Clarion
variable again, like this (part of the WindowProc of the sublassed window):
DATA
SomeReference &MyClass
CODE
SomeReference &= (GetProp(hWnd, "MyClassUniqueString"))
case Msg
of WM_PAINT
SomeReference.OnPaint(...)
of WM_SETFOCUS
SomeReference.OnSetFocus(...)
of WM_KILLFOCUS
SomeReference.OnKillFocus(...)
end
I've started rewriting my Sys* product series using this technique and
haven't experienced any problems yet...
HTH!
Jens
--
Jens Weiermann
solid software
http://www.solidsoftware.de
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