From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2003-05-20T16:51:28+09:00
Subject: problem deleting item on a TkCanvas

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
    @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