From: Morton Goldberg <m_goldberg@...>
Date: 2006-09-05T20:43:01+09:00
Subject: Re: How to properly bind context menus to canvas in Ruby/Tk?


On Sep 3, 2006, at 10:40 AM, Josef Wolf wrote:

> Hello!
>
> I am trying to bind context-menus to a Tk canvas.  The canvas  
> itself should
> have a context menu, giving the ability to create new objects.  In  
> addition,
> every object should have its own context menu so that the object  
> can be
> modified/deleted.  This is what I'm doing:
>
>   #! /usr/bin/ruby
>   require 'tk'
>   $-w = 1
>
>   root = TkRoot.new
>   canvas = TkCanvas.new.pack
>
>   # This is the context menu for the canvas to create new objects
>   #
>   menu=TkMenu.new
>   menu.add('command', 'label'=>'New Foo', 'command'=>proc{p "new  
> foo"})
>   menu.add('command', 'label'=>'New Bar', 'command'=>proc{p "new  
> bar"})
>
>   # canvas binding
>   canvas.bind("Button-3") { |e| evt=e; menu.popup(e.x_root,  
> e.y_root) }
>
>   # Now create a new object and bind to it a context menu to modify/ 
> delete
>   # the object
>   #
>   rect = TkcRectangle.new(canvas, 0, 0, 50, 50, "fill"=>"white")
>   menu=TkMenu.new
>   menu.add('command', 'label'=>'Edit',   'command'=>proc{p "edit"})
>   menu.add('command', 'label'=>'Delete', 'command'=>proc{p "del"})
>
>   # object binding
>   canvas.itembind(rect, "Button-3") { |e| menu.popup(e.x_root,  
> e.y_root) }
>
>   Tk.mainloop
>
> Unfortunately, this don't work as desired.  As soon as the binding  
> to the
> object is done, the canvas binding seems to be overridden.  Even when
> right-klicking on empty space in the canvas, the object's menu is  
> invoked.
>
> Any ideas what I am doing wrong here?

I tried running your code on my system which is OS X 10.4.7 running  
Ruby 1.8.2, and I don't see what you report. What I see is following:

* Right-clicking away from the the rectangle, the canvas' contextual  
menu pops-up.
* Right-clicking on the rectangle.
     ** The rectangle's contextual menu pops-up.
     ** When the rectangle's menu is dismissed, the canvas'  
contextual menu pops-up.

With a small tweak, I was able to keep the canvas' contextual menu  
from popping up when the the rectangle is right-clicked. So what I  
have now running on my system works as you expected.

Regards, Morton

P.S. Just in case you want to compare what I am running with your own  
code.
<code>
#! /usr/bin/ruby -w
# Date: September 5, 2006
#
# Contextual menus on a canvas

require 'tk'

DEBUG = []
RIGHT_BUTTON = "Button-2" # On OS X right button is Button-2.

begin
    root = TkRoot.new {title 'Ruby Tk'}
    canvas = TkCanvas.new.pack
    handled_by_rect = false

    # This is the context menu for the canvas to create new objects
    menu1=TkMenu.new
    menu1.add('command', 'label'=>'New Foo', 'command'=>proc{p "new  
foo"})
    menu1.add('command', 'label'=>'New Bar', 'command'=>proc{p "new  
bar"})

    # Canvas binding
    canvas.bind(RIGHT_BUTTON) do |e|
       if handled_by_rect
          handled_by_rect = false
       else
          menu1.popup(e.x_root, e.y_root)
       end
    end

    # Now create a new object and bind to it a context menu to modify/ 
delete
    # the object
    rect = TkcRectangle.new(canvas, 50, 50, 100, 100, "fill"=>"white")
    menu2=TkMenu.new
    menu2.add('command', 'label'=>'Edit',   'command'=>proc{p "edit"})
    menu2.add('command', 'label'=>'Delete', 'command'=>proc{p "del"})

    # Rectangle binding
    canvas.itembind(rect, RIGHT_BUTTON) do |e|
      menu2.popup(e.x_root, e.y_root)
      handled_by_rect = true
    end

    # Set initial window geometry; i.e., size and placement.
    win_w, win_h = 300, 200
    # root.minsize(win_w, win_h)
    win_lf = (root.winfo_screenwidth - win_w) / 2
    root.geometry("#{win_w}x#{win_h}+#{win_lf}+50")

    # Make Cmnd+Q work as expected on OS X.
    root.bind('Command-q') {Tk.root.destroy}

    Tk.mainloop
ensure
    puts DEBUG unless DEBUG.empty?
end
</code>