PerlTk - Trying to figure out waitVariable command

Author

Trying to figure out waitVariable command

Golgi !

2004-09-19, 3:56 am

Can't seem to figure out waitVariable command. This test simply hangs at
the command, although the referenced variable was changed right before it.

#!/usr/local/bin/perl -w
use Tk;
use strict;

my $mw = MainWindow->new;
my $button = $mw -> Button(-text => 'Test waitVariable',
-command => sub {
my $status = &subroutine('First Value');
print "Status: $status\n";
}) -> pack();
MainLoop;

sub subroutine
{
my $var = shift;
print "Value = $var\n";

$var = 'Second Value';
print "Value = $var\n";

$mw->waitVariable(\$var); # <- Hangs here. Is $mw ok?
return $var;
}

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Wolfgang Hommel

2004-09-19, 9:00 am

Hello Golgi,

> Can't seem to figure out waitVariable command. This test simply hangs at
> the command, although the referenced variable was changed right before it.

It doesn't "hang", it simply waits for the variable being changed.

Your example is lacking any way to change the variable content, e.g.
through a widget, a Tk or file event, a background process, ... so
waitVariable never returns, because the variable never changes after
waitVariable gets invoked.

Regards,
Wolfgang

Hans Jeuken

2004-09-19, 3:57 pm

On Sunday 19 September 2004 03:27, Golgi ! wrote:
> Can't seem to figure out waitVariable command. This test simply hangs at
> the command, although the referenced variable was changed right before it.
>

Try this instead:

#!/usr/local/bin/perl -w
use Tk;
use strict;

my $mw = MainWindow->new;
my $var;

$mw -> Button(
-text => 'Initialize',
-command => sub {
$var = 'initial value';
print "variable initialized\n";
$mw->waitVariable(\$var);
print "variable has changed to: $var,\ncontinuing MainLoop\n";
}
)->pack(-fill => 'x');

$mw->Button(
-text=> "Change value",
-command => sub {
print "Changing variable\n";
$var = "another value"
}
)->pack(-fill => 'x');

MainLoop;
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Golgi !

2004-09-19, 3:57 pm

Nice. Thanks for the test code. It works and I'll study it a bit further
to better understand it.

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Lidie Steve

2004-09-19, 8:58 pm

On Sep 19, 2004, at 2:02 PM, Golgi ! wrote:

> Nice. Thanks for the test code. It works and I'll study it a bit
> further to better understand it.

In your original code you first changed the variable and then tried a
waitVariable(). But you need to invoke waitVariable() *before*
changing the variable: that's how the method is defined. No tachyon
messages in Perl/Tk programming ;)

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zentara

2004-09-20, 9:00 pm

On Sun, 19 Sep 2004 14:02:34 -0400, "Golgi !" <golgi_perl@msn.com>
wrote:

>Nice. Thanks for the test code. It works and I'll study it a bit further
>to better understand it.

Hi, here is a simpler example which is clearer.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = MainWindow->new();

my $count = 0;

# To have a program wait until a variable's value is
# changed, call waitVariable:
$mw->after(5000,[sub{$count++}]);

$mw->waitVariable(\$count);
# event loop will wait here until $count changes

my $mw1 = MainWindow->new();

MainLoop;
__END__

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