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

my $mw = MainWindow->new;
my $tree = $mw->Scrolled('Tree')->pack(qw/-expand 1 -fill both/);

foreach(1 .. 100) {
      $tree->add($_, -text => "Line $_");
}


# you must update the tree first
# before the yview works
$tree->update;
$tree->yview( moveto => .5 );

# or it will always work from a widget
# command after the gui has visibility

$mw->Button( # always works because you have visibility
    -text    => "move it (this works)",
    -command => sub { $tree->yview( moveto => 1 ); }
)->pack;

MainLoop;
[download]

Welcome back! ;)

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!}

I finally logged in ... (facepalm) ... in case the question comes up, $TK{'vl'} is a Tk::Frame which is "view left" or 'vl' in the Tk GUI I'm building. Or trying to build. Or failing at. It depends on your point of view, and visual acuity.

# Create a left hand view frame in the workspace frame - for the tree
$TK{'vl'}=$TK{'ws'}->Frame()->pack(-side   => 'left',
                                   -anchor => 'n',
                                   -expand => 0,
                                   -fill   => 'both');
[download]

Similarly 'ws' is a workspace Tk::Frame inside the main window. But that's probably not important.

I create a button to report the tree xview value and just was lost even more ...

  my @pos=$TK{'perltree'}->xview();

  my $pos=shift(@pos);

  print 'xview=' . join(",", $pos) . "\n";
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Thanks from nzsvz9

It was the update before the xview that did it!

Thanks Japh!