From: Hidetoshi NAGAI <nagai@...>
Date: 2005-06-23T12:38:19+09:00
Subject: Re: tk canvas question

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"'.
-- 
Hidetoshi NAGAI (nagai@ai.kyutech.ac.jp)