Understanding Tk Listbox in ruby - ruby

Question

I'm trying to make a small program to mung some data into usable form. One thing I'd like it to do is to be able to select some files and perform actions on them, so I thought i'd use the listbox object in Tk to do that. I want to be able to open a file and see its filename displayed in the listbox. As far as I've read this is precisely what using listvariable in the listbox is for. Yet when I run my code the listbox is never updated (although items already in the listvariable variable are displayed fine).
So here's a close to MWE for this. What am I doing wrong, and what fundamental idea have I misunderstood?
require 'tk'
require 'tkextlib/tile'
$path_list = []
$populate_list = TkVariable.new( $path_list )
def get_file
file = Tk.getOpenFile
file = open(file) unless file.empty?
path = File.basename(file, ".out")
if $path_list.include?(path)
Tk.messageBox(
'type' => "ok",
'icon' => "warning",
'title' => " - Minimum Working Example - ",
'message' => "This file has already been added! Nothing was added to the list"
)
else
$path_list.push(path)
end
end
root = TkRoot.new {title "- Minimum Working Example -"}
frame = Tk::Tile::Frame.new(root) {padding "3 3 12 12"}.grid( :sticky => 'nsew') # 'north south east west'
TkGrid.columnconfigure root, 0, :weight => 1; TkGrid.rowconfigure root, 0, :weight => 1
$file_listbox = Tk::Listbox.new(frame) {
listvariable $populate_list}.grid( :column => 1, :row => 0, :rowspan => 6)
Tk::Tile::Button.new(frame) {
width 15; text 'Open file...'; command {get_file}}.grid( :column => 0, :row => 1)
Tk.mainloop
Do I maybe have to write it in some other order?

Answer 1

Just add one line of code:
$populate_list.value = $path_list
under this one:
$path_list.push(path)
It works for me, although looks weird.
TkVariable create a proxy for you ruby variable, thus bridge your ruby var references with Tk widgets. But i don't know why changes in proxy var don't affect the var it points to. I'm not sure whether it should do that automatically.