From: Ron Jeffries <ronjeffries@...>
Date: 2001-03-21T08:10:02+09:00
Subject: [ruby-talk:12989] Re: TextBox ListBox (Access to @vars)

OK, here's what's confusing us now. we have code like what's included
at the end here. (sorry it's so big, I'm not sure what to clip to
leave it still working):

Basically we are building a hashview object that when created, creates
a window upon initialize. The window has a listbox and a textbox as
before. When you click a key, the value displays. You can define a new
value or redifine an old one by typing the association in the text
window and typing Control-s. For example 
	x => this is a new value for x

So our object wants to have the hash (we call it a dictionary because
we are old-fashioned) as an instance variable. (We'll be opening the
view on a TopLevel or something in the future, so there can be more
than one.)

Now when you add an item, we have to refresh the list box from the
keys of the dictionary. We have set up a general bind of Control-s, so
that code needs access to the listbox. 

We originally had the listbox as a local variable in the setup of the
frame (copying from one of the demos), and learned that we had to
define the local (keyListbox) as nil OUTSIDE the proc, to get access
to it later on, in the code that inserts hash keys into the list box.

We wanted to implement the refreshList method on HashBrowserView, so
we wanted to change the local keyListbox to an instance variable. The
obvious change, replacing keyListbox with @keyListbox, doesn't work.
We are guessing that the @variables inside the proc are defining
themselves into the proc.

So the only way we could think of to get the variable set was to write
a setter for the instance variable and send it:
	defineWidget(keyListbox)

As I think about it now, we could probably put an explicit scope on
the variable, ala
	HashBrowserView::@keyListbox
and just use that everywhere. I'll try that if I can figure out the
syntax ...

Are we on the right track here? Is it true that @variable inside a
proc defines an instance variable on the proc instance? Is there a
better, cleaner way to do what we're trying to do?

Thanks!

Ron

==================================
require 'tk'
require 'tkencoding'
require 'tkafter'

class HashBrowserView
    def initialize(aDictionary)
        @dictionary = aDictionary
        @methodListWidget = nil
    
        hashBrowserView = TkRoot.new {|w|
          title("Dictionary Browser")
          #positionWindow(w)
        }
        hashBrowserView.bind("Control-s", proc {save})
        keyListbox = nil
        TkFrame.new(hashBrowserView, 'borderwidth'=>10) {|w|
          s = TkScrollbar.new(w)
          keyListbox = TkListbox.new(w) {
            setgrid 1
            width  10
            height 12
            selectmode 'single'
            yscrollcommand proc{|first,last| s.set first,last}
          }
          s.command(proc{|*args| keyListbox.yview *args})
          s.pack('side'=>'right', 'fill'=>'y')
          keyListbox.pack('side'=>'left', 'expand'=>1, 'fill'=>'both')
        }.pack('side'=>'top', 'expand'=>'yes', 'fill'=>'y')

          @dictionary.keys.each { |key|
            keyListbox.insert('end', key) }

         @textBox = TkText.new(hashBrowserView, 'height'=>10)
         @textBox.pack

        keyListbox.bind('ButtonRelease-1', proc{
            sel = keyListbox.curselection
            selection = keyListbox.get(sel)
            @textBox.delete('1.0','end')
            @textBox.insert('1.0', @dictionary[selection])})
        defineWidget(keyListbox)
    end
    def defineWidget(aWidget)
        @methodListWidget = aWidget
    end
    def save
        value = @textBox.get('1.0','end')
        value =~ /([\w+]) +=> +(.+)/
        @dictionary[$1] = $2
        refreshList
    end
    def refreshList
        @dictionary.keys.each { |key|
            @methodListWidget.insert('end', key) }
    end
end 

dictionary = {'a'=>'this is the text for a',
    'b'=>'and here is good old b' }

hashBrowser = HashBrowserView.new(dictionary)
Tk.mainloop

Ronald E Jeffries
http://www.XProgramming.com
http://www.objectmentor.com