From: Joe Van Dyk <joevandyk@...>
Date: 2005-06-23T13:01:10+09:00
Subject: Re: tk canvas question

On 6/22/05, Hidetoshi NAGAI <nagai@ai.kyutech.ac.jp> wrote:
> From: Joe Van Dyk <joevandyk@gmail.com>
> Subject: Re: tk canvas question
> Date: Thu, 23 Jun 2005 04:03:26 +0900
> Message-ID: <c715e6405062212036981cfe7@mail.gmail.com>
> > Apparently, I can just delete the group.  I'm not sure why it didn't
> > work before, but it is now.
> 
> The reason is that "add" method call adds no canvas-tag to target
> widgets.
> 
> TkcGroup has no "add" instance method.
> Then, Ruby/Tk assumes that it is configuration of "-add" option.
> Of course, canvas items don't have such option.
> However, if the target of configuration is a canvas-tag which is not
> assigned to any items, Tk generates no error and returns an empty
> string.
> So, TkcGroup#add does nothing and returns "" without errors.
> 
> TkcGroup#include works properly, that is, adds its canvas-tag to
> target widgets.
> After that, TkcGroup#add will raise an exception 'unknown option
> "-add"'.

Very informative.  Thank you!