| Re: border around draw widget [message #50362 is a reply to message #50360] |
Wed, 27 September 2006 15:23   |
JD Smith
Messages: 850
Registered: December 1999
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Senior Member |
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On Wed, 27 Sep 2006 23:35:34 +0200, Laurens wrote:
> Thanks very much for that explanation!
> Could you tell me how to make such a widget-object? It sounds like
> something I was already thinking about...
It sounds fancier than it is. It's basically an object, which:
1. Sets up a widget heirarchy in the normal way (usually in its Init
method).
2. Saves its "state" information not in a structure in a UVALUE but in
the class data itself (e.g. self.*).
3. Calls XManager (often, but not necessarily, in its Init method) to
generate events on that widget heirarchy.
4. Uses the trick I outline to inject the events flowing forth from
the widgets created to some class method (often named "Event").
The main advantages of this method:
1. You get state information "for free", quite nicely mapped to class
data.
2. You automatically avoid common blocks for state info, with their
associated collision risks if multiple identical widgets run at the
same time.
3. You are never left with state information "in the air", if you use
/NO_COPY to be efficient when retrieving your state structure from
a UVALUE. This greatly aids debugging, since crashes to the code
usually can be recovered from with a simple RETALL.
4. You quickly realize that the normal event flow embodied in "normal"
widget prgramming is limiting, and can roll your own communication
among objects that suits your needs. This is particularly useful
if you have many different perhaps unrelated application components
that need to communicate with eachother.
A schematic usage would be:
oDraw=obj_new('SelectableDrawPane',base)
which would place a new compound widget into base. It might implement
some methods "Select" and "DeSelect", or you could have it trap the
selection "clicks" and automagically select/deselect itself. Once you
have the apparatus in place, you can then have fun implementing other
methods for your object, drawing and erasing, etc.
I should note that none of this is necessary to use the "base on top
of a base" trickery I outlined before, it just makes it easier and more
powerful.
JD
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