From: MENON Jean-Francois <jean-francois.menon@...>
Date: 2003-05-21T11:15:44+09:00
Subject: Re: problem deleting item on a TkCanvas

Phil Tomson wrote:
> 
> I've got a TkCanvas where I initially draw a vertical line at the far left
> of the canvas.  I've bound the left mouse button such that when pressed a
> new vertical line is drawn at that x location, and the old line is
> _supposed_ to be erased (deleted).  But the old line is not being deleted.
> 
> Here's the code:
> 
> require 'tk'
> class SigWave
>   def initialize(root,signame)
>     @frame = TkFrame.new(root).pack('anchor' => 'e','padx'=>1,'pady'=>1)
>     @name  = TkLabel.new(@frame){text "#{signame}"}.pack('side'=>'left')
>     @canvas = TkCanvas.new(@frame)
>     @canvas.configure  'height'=> 20
>     @canvas.pack('side'=>'right', 'fill'=>'x')
>     @cursor=TkcLine.new(@canvas, 1,0,1,20).fill('blue')
>     @canvas.bind('1',proc{|e| draw_cursor(e.x) })
>     draw_cursor(1)
>   end
> 
>   def draw_cursor(x)
>     @canvas.delete(@cursor) #<= this seems to do nothing

use @cursor.delete instead ?


>     @cursor=TkcLine.new(@canvas, x,0,x,20).fill('blue')
>   end
> end
> 
> root  = TkRoot.new() {title "Waveform" }
> SigWave.new(root,'signame')
> 
> Tk.mainloop
> #end of code
> 
> Am I doing the @canvas.delete correctly?
> 
> Phil


I would do a @cursor.coords(..);Tk.update instead. I noticed some
memory problems when creating/deleting a big number of canvas items with
ruby.

regards,
jf