Message-ID: <42FBE5FC.8010103 at rftp.com>
Date: Thu, 11 Aug 2005 16:57:48 -0700
From: Robert Roessler <robertr at rftp.com>
Organization: Robert's High-performance Software
MIME-Version: 1.0
To: romildo at uber.com.br
CC: lablgtk at math.nagoya-u.ac.jp
Subject: Re: How to define a customized button
References: <20050811120246.GA10175 at malaquias>
In-Reply-To: <20050811120246.GA10175 at malaquias>
Content-Type: text/plain; charset=us-ascii; format=flowed
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romildo at uber.com.br wrote:

> I want to learn how to define customized widgets
> with lablgtk. For that I would like to define a
> new button widget which just automatically encloses
> its text label inside square brackets.
> 
> Attached is my attempt in doing so. But it does not
> compile.
> 
> As I did not find any explanation on how to
> define customized widgets, I am lost on how to
> do it. Maybe someone kind enough could show
> me how to implement this simple program.

How about

--------------------
class my_button obj = object (self)
   inherit GButton.button obj as super
   method set_label t = super#set_label ("[" ^ t ^ "]")
end

let pack_return create p ?packing ?show () =
   GObj.pack_return (create p) ~packing ~show

let my_button ?label =
   let label =
     match label with
     | None -> None
     | Some t -> Some ("[" ^ t ^ "]") in
   GtkButton.Button.make_params [] ?label ~cont:(
   pack_return (fun p -> new my_button (GtkButton.Button.create p)))
--------------------

To [minimally] test it, you just need

--------------------
let delete_event ev = false

let main () =
   let w = GWindow.window ~title:"Test" () in
   let b = my_button ~label:"my_button" () in
   let v = GPack.vbox ~packing:w#add () in
   v#pack b#coerce ~expand:true;
   ignore (w#event#connect#delete ~callback:delete_event);
   ignore (w#connect#destroy ~callback:GMain.Main.quit);
   w#misc#show_all ();
   GMain.Main.main ()

let _ = main ()
--------------------

Yes, it is something of a hack... :)

But it does show the classic "inheritance with method override" 
approach available with objects - the only complicated part about the 
my_button creation function is handling the optional label - and there 
may be a cleaner way of doing this.

Robert Roessler
robertr@rftp.com
http://www.rftp.com