TK Pane->yview not working?

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

Trying to debug my script, I broke it down to bare minimum:

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

my $mw = MainWindow->new( );
$mw->minsize(200,300);

my $pane = $mw->Scrolled( 'Pane',
    -scrollbars => 'e',
    -border => 2,
    )->pack(-fill=>'both', -expand=>1);

foreach my $x (1..100) {
    my $label = $pane->Label(
        -text    => $x,
    )->pack(-side=>'top', -fill=>'x', -expand=>0);
#    $pane->yview(moveto => 1);
}
MainLoop;
[download]

Above script suppose to create a Pane, then populate it with 100 labels.
So far so good.

Uncommenting the line $pane->yview($label);, it is suppose to scroll to the bottom.
But I get this error:

Can't call method "Call" on an undefined value at C:/Perl/site/lib/Tk/Pane.pm line 346.

What is wrong?

According to documents (http://search.cpan.org/~srezic/Tk/Tk/Pane.pm):
$pane->yview(moveto => 1) Is how to scroll to the very bottom but it is not doing so. Why?

Comment on TK Pane->yview not working? Select or Download Code

Replies are listed 'Best First'.
Re: TK Pane->yview not working? by tybalt89 (Monsignor) on Apr 22, 2018 at 20:39 UTC
`moveto => 1` works if you do it after the geometry manager has run, which seems to be the trick for both of your problems. `#!/usr/bin/perl # http://perlmonks.org/?node_id=1213368 use strict; use warnings; use Tk; use Tk::Pane; my $mw = MainWindow->new( ); $mw->minsize(200,300); my $pane = $mw->Scrolled( 'Pane', -scrollbars => 'e', -border => 2, )->pack(-fill=>'both', -expand=>1); foreach my $x (1..100) { my $label = $pane->Label( -text => $x, )->pack(-side=>'top', -fill=>'x', -expand=>0); } $mw->after(1, sub { $pane->yview(moveto => 1) } ); MainLoop;` [download]	[reply] [d/l] [select]
Re: TK Pane->yview not working? by tybalt89 (Monsignor) on Apr 22, 2018 at 14:30 UTC
`#!/usr/bin/perl # http://perlmonks.org/?node_id=1213368 use strict; use warnings; use Tk; use Tk::Pane; my $mw = MainWindow->new( ); $mw->minsize(200,300); my $pane = $mw->Scrolled( 'Pane', -scrollbars => 'e', -border => 2, )->pack(-fill=>'both', -expand=>1); foreach my $x (1..100) { my $label = $pane->Label( -text => $x, )->pack(-side=>'top', -fill=>'x', -expand=>0); $mw->update; $pane->yview($label); } MainLoop;` [download]	[reply] [d/l]


Think about Loose Coupling
	PerlMonks