how to change the status of a checkbutton interactively

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Subject	how to change the status of a checkbutton interactively
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Hi all, 

I am new to tk. I try to build a simple GUI with several widgets following the tutorials from this website:http://www.tkdocs.com/tutorial/widgets.html#checkbutton
 
 One of the widgets I copy from website is checkbutton as following:

 
require 'tk'
 require 'tkextlib/tile'
 
 root = TkRoot.new {title "Feet to Meters"}
 $measureSystem = TkVariable.new
 check = Tk::Tile::CheckButton.new(root) {
     text 'Use Metric'; 
     command 'metricChanged'; 
    variable $measureSystem; 
     onvalue 'metric';
     offvalue 'imperial';
    pack
     }
 
 Tk.mainloop
 
 when I check the checkbutton, I get an error message as following:
 
NameError: undefined local variable or method `metricChanged' for main:Object
 ---< backtrace of Ruby side >-----
 C:/Ruby200-x64/lib/ruby/2.0.0/tk.rb:1456:in `cb_eval'
 C:/Ruby200-x64/lib/ruby/2.0.0/tk.rb:1456:in `eval_cmd'
 C:/Ruby200-x64/lib/ruby/2.0.0/tk.rb:1456:in `cb_eval'
 C:/Ruby200-x64/lib/ruby/2.0.0/tk.rb:1403:in `call'
 C:/Ruby200-x64/lib/ruby/2.0.0/tk.rb:1599:in `block in callback'
 C:/Ruby200-x64/lib/ruby/2.0.0/tk.rb:1598:in `catch'
 C:/Ruby200-x64/lib/ruby/2.0.0/tk.rb:1598:in `callback'
 C:/Ruby200-x64/lib/ruby/2.0.0/tk.rb:1305:in `mainloop'
 C:/Ruby200-x64/lib/ruby/2.0.0/tk.rb:1305:in `block in <module:TkCore>'
 ---< backtrace of Tk side >-------
    invoked from within
 "rb_out c00001"
    invoked from within
 ".w00000 invoke "
    invoked from within
 ".w00000 instate !disabled { .w00000 invoke } "
    invoked from within
 ".w00000 instate pressed { .w00000 state !pressed; .w00000 instate !disabled { .w00000 invoke } } "
    (command bound to event)
 
 so my question is that why this happens? How come I cannot set the check or uncheck  from user end or set its status interactively?

 
 Thank you so much in advance for your help.

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how to change  the status of a checkbutton interactively chen1069osu@gmail.com - 2014-06-02 07:42 -0700

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