Height of a label widget in Tk

Jouke has asked for the wisdom of the Perl Monks concerning the following question:

I tried to determine the height of a label object, but every time I run the code it returns '1', unless I run it using the Tk debugger (perl -d:ptkdb script.pl) in which case it returns '20', which is the correct value.

This is the code:

#!/usr/bin/perl -w
use strict;
use Tk;
my $main = MainWindow->new(-background => "white");
$main->title("test program");
my $mainframe = $main->Frame(-background => "white")->pack();

my $label=$main->Label(-text => "test text", -background => "white")->
+pack;

print $label->height();

MainLoop()
[download]

So my obvious question is why I don't get the correct value ?!?!

Jouke Visser, Perl 'Adept'

Comment on Height of a label widget in Tk Select or Download Code

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Re: Height of a label widget in Tk by busunsl (Vicar) on May 25, 2001 at 13:45 UTC
The call to MainLoop will pack the window and calculate the size of the widgets. Create a Button to call a sub, it will give you the correct height. The Tk-Debugger has it's own MainLoop, well sort of. So height will be printed correctly. Update: Putting a `$main->update()` before the print will work.	[reply] [d/l]
Re: Re: Height of a label widget in Tk by Jouke (Curate) on May 25, 2001 at 20:32 UTC
Your last suggestion works like a charm! Thanx! ++busunsl! Jouke Visser, Perl 'Adept'	[reply]
Re: Height of a label widget in Tk by TheoPetersen (Priest) on May 25, 2001 at 17:04 UTC
In general you can't trust the values of attributes like this until the widget (or window) is displayed. The `$w->waitVisibility` method allows you to let the widget get displayed and then check matters of interest. Inside of `$w->waitVisibility` Tk does updates and processes other events until the widget receives a Visibility event. If you want to handle this kind of thing asynchronously you could look at hooking into that event yourself.	[reply] [d/l] [select]