RE: [platform-swt-dev] Subclassing Widgets..

[Arnaud De Muyser <ademuyser@xxxxxxxxxx>]

As lots of SWT widgets classes (except
Control and Composite) are tagged using "final" java keyword,
nobody can subclasse them ...
In addition, there are a runtime check
for subclassing too ... the method is ... Widget.checkSubclass().

The good idea is to subclass only Control
and Composite, and uses Listeners (paint,/mouse) to try
to do the works for other ... but I'm
right this is too poor solution to do all what we want (I'd the same problem
because before using SWT we used Trolltech's
Qt C++ framework and I was really disturbed by SWT limitation
on subclassing).

good luck,

Arnaud.

"R.J. Lorimer" <rjlorimer@xxxxxxxxxxxxxxxx>
Sent by: platform-swt-dev-admin@xxxxxxxxxxx

11/23/2004 03:03 PM

Please respond to
platform-swt-dev

To	<platform-swt-dev@xxxxxxxxxxx>
cc
Subject	RE: [platform-swt-dev] Subclassing Widgets..

Eric,

Maybe I am wrong (I haven't tried for a long while), but I was under the
impression that runtime checks were in place that prevented subclassing
in
many cases.

Is this not the case anymore?

-----Original Message-----
From: platform-swt-dev-admin@xxxxxxxxxxx
[mailto:platform-swt-dev-admin@xxxxxxxxxxx] On Behalf Of Eric Clayberg
Sent: Tuesday, November 23, 2004 7:38 AM
To: platform-swt-dev@xxxxxxxxxxx
Subject: RE: [platform-swt-dev] Subclassing Widgets..

Samir.

>I read the document and understand the consequences of subclassing.
But 
>the Subclassing is a feature of any object-oriented language and when
>someone creates a subclass he/she is aware of consequences the 
>subclassing can have. In my case I wanted to subclass the component
to 
>add some extra features like my custom table with few predefined menu
>whose functionality is fixed. These things can be achieved from 
>composition but that is not the right way to do in case of Java.

If you are aware of the consequences and accept that responsibility, the
go
ahead and subclass any widgets that you like. Just be aware that your
subclass might not be portable across platforms and might break in a future
release. Aside from that, most SWT widgets can be subclassed quite easily.

-Eric 


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