From: Phlip <phlipcpp@...>
Date: 2003-05-27T15:04:23+09:00
Subject: Tk: Call mainloop twice

Rubies:

The following code, when the user hits <Alt+F4> or clicks the little close
gadget on your window, destroys the TkRoot singleton, so everything below
the first Tk.mainloop won't work:

 require 'tk'

 canvas = TkCanvas.new() {width(400);height(300) }
 TkcText.new(canvas, 100, 200) { text 'hello world' }
 canvas.grid

 canvas.bind('Destroy') { |event|
  puts "going down"
  return if event.widget != @canvas
  Tk.quit
  }

 Tk.mainloop

 canvas = TkCanvas.new() {width(400); height(300)  }
 TkcText.new(canvas, 200, 100) { text 'hello world' }
 canvas.grid
 Tk.mainloop

The second call to TkCanvas.new dies with:

bgerror failed to handle background error.
    Original error: c:/ruby/lib/ruby/1.7/tk.rb:358:in `call': return from
proc-closure
    Error in bgerror: can't invoke "toplevel" command:  application has been
destroyed

Witness my feeb attempt to tell the Tk.mainloop to gracefully exit instead
of destroy everything inside itself. I tried to bind to the Destroy event.

We may presume that the Destroy event itself takes down the Tk context. In
this case, maybe there is some other event I can bind to, or some other
binding site.

I would prefer, for elaborate & irrelevant reasons, not to just add a
stinkin' button one can click on to call the Tk.quit. And experiments with
Tk.callback_break likewise bomb. Experiments opening another window, so the
first Tk.mainloop would still feel useful when the canvas goes down, also
failed.

--
  Phlip
    http://www.c2.com/cgi/wiki?TestFirstUserInterfaces