From: Hidetoshi NAGAI <nagai@...>
Date: 2006-02-28T00:13:47+09:00
Subject: Re: Ruby/Tk: How to access surrounding class from Tk Callback?

From: u235321044@spawnkill.ip-mobilphone.net (Ronald Fischer)
Subject: Ruby/Tk: How to access surrounding class from Tk Callback?
Date: Mon, 27 Feb 2006 21:18:35 +0900
Message-ID: <l.1141041120.1069274902@proxy21-ic-ext.mch.sbs.de>
>     @root=TkRoot.new() { title "My Form" }
>     action_button=TkButton.new(@root) { 
>       text "Action!" 
>       command {
>         # Do something with @root and @foo
>         puts @root.foo # DOES NOT WORK
>       }
>     }

It may be a FAQ.
A block given to <TkWidget-class>.new method is 
evaluated by <the widget>.instance_eval(<the block>).
That is, in the block, 'self' is the widget object.
So, @root in your button's command is an instance variable 
of the button widget.
To avoid it, you have to give attention to scope of variables.
For example, 
------< example 1 >------------------------------------------
  def initialize(...)
    foo = @foo=1234
    ...
    root = @root = TkRoot.new() { title "My Form" }
    action_button=TkButton.new(@root) { 
      text "Action!" 
      command {
        # use local variables
        puts foo   # same as @foo
        puts root  # same as @root
      }
    }
    action_button.pack("side" => "right");
  end
-------------------------------------------------------------
------< example 2 >------------------------------------------
  def initialize(...)
    @foo=1234
    ...
    @root = TkRoot.new() { title "My Form" }
    action_button=TkButton.new(@root, 
                               :text=>"Action!",
                               :command=>proc{
                                  puts @foo
                                  puts @root
                               })
    action_button.pack("side" => "right");
  end
-------------------------------------------------------------
------< example 3 >------------------------------------------
  def initialize(...)
    @foo=1234
    ...
    @root = TkRoot.new() { title "My Form" }
    cmd = proc{
      puts @foo
      puts @root
    }
    action_button=TkButton.new(@root) { 
      text "Action!" 
      command cmd
    }
    action_button.pack("side" => "right");
  end
-------------------------------------------------------------
-- 
Hidetoshi NAGAI (nagai@ai.kyutech.ac.jp)