To: rich at annexia.org
Cc: lablgtk at kaba.or.jp
Subject: Re: Inherit my own widget from another
In-Reply-To: <20030704155328.GB28782 at redhat.com>
References: <20030704155328.GB28782 at redhat.com>
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Message-Id: <20030705110338P.garrigue at kurims.kyoto-u.ac.jp>
Date: Sat, 05 Jul 2003 11:03:38 +0900
From: Jacques Garrigue <garrigue at kurims.kyoto-u.ac.jp>
Lines: 51

From: Richard Jones <rich at annexia.org>

> I'm getting a bit lost trying to create my own widget. The widget
> I want to create will have a drawing area & a scrollbar, contained
> inside a vbox. It seemed a good idea, therefore, to inherit from
> the box class. This is as far as I've got:
> 
> open GObj
> open GContainer
> open GPack
> 
> class graph obj =
>   object (self)
>     inherit box obj
>     val da = GMisc.drawing_area ~packing:self#add ()
>     val drawable = da#misc#realize (); new GDraw.drawable da#misc#window
>     method test = "test"
>   end
> 
> let graph ?homogeneous ?spacing ?border_width ?width ?height
>     ?packing ?show () =
>   let w = Box.create dir ?homogeneous ?spacing () in
>   Container.set w ?border_width ?width ?height;
>   pack_return (new graph w) ~packing ~show
> 
> 
> There's a couple of problems here, not least the fact that it doesn't
> compile (because the initialization of 'da' can't refer to 'self',
> although it needs to). Also I'm having to copy in lines of code
> directly from gPack.ml, which doesn't help with maintainability.

Actually, inheriting to create a meta-widget is a bad idea: your
widget is not a box in any useful meaning (you do not expect people to
add stuff in it). Inheriting only from Gobj.widget and delegating is
much better.

class graph ?width ?height ?packing ?show () =
  let sw = Gbin.scrolled_window ?width ?height ?packing ?show () in
  let da = GMisc.drawing_area ~packing:sw#add () in
  object
    inherit widget sw#as_widget
    val drawable = lazy (new GDraw.drawable da#misc#window)
    method sw = sw
    method da = da
    method drawable = Lazy.force drawable
    method test = "test"
  end

You see the idea?

    Jacques