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

I am trying to use Perl's Tk module for guis. From what I understand it should be possible to generate events programatically which will then will trigger any listeners on a widget. So i did the following:

 use Tk;
my $mw = new MainWindow; 
my $label = $mw -> Label(-text=>"Hello World") -> pack();
my $button = $mw -> Button(-text => "Quit");
$button->bind('<ButtonPress-1>' => \&myexit);
$button->pack;
MainLoop;
$button->eventGenerate('<ButtonPress-1>');

sub myexit
{
exit;
}

[download]

Here I create a window with a label and a button and whenever the button is clicked the program should exit. It works perfectly when actually clicking the button. When trying to generate a click, nothing happens. I have also read about virtual events, are these a special kind of events, so that I can generate only events of that type? What I wonder is whether I am unable to generate builtin events like keypress and such. Any help would be very welcome.

Hmm, I just realized that maybe MainLoop is halting the entire program, thus eventGenerate is never reached. But in that case eventGenerate seems rather pointless.

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Re: how to use eventGenerate in Tk
by choroba (Cardinal) on Oct 31, 2018 at 12:19 UTC
    Yes, you MainLoop blocks the program, so putting Tk-related stuff below it makes no sense. You can for example schedule an event to happen one second after the application was started: 
    $mw->after(1000 => sub { $button->eventGenerate('<ButtonPress-1>') });
MainLoop();

    [download]

    ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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      Thank you, so if I wish to draw a dynamic graph, then firing an event to make the graph redraw is not an option.
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        Why, of course it is. You just need to fire it from an "after" or "repeat", or even a "fileevent" (when new data arrive).

        ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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Re: how to use eventGenerate in Tk
by zentara (Cardinal) on Oct 31, 2018 at 12:29 UTC
    Hi, first off, you have a glaring error in your program flow. Once the line MainLoop is encountered, no further lines are processed until the MainLoop ( the Tk event loop system) is destroyed. So you never call eventGenerate until the Tk eventloop is gone, so it probably tries to run but throws an error. 
    #!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = new MainWindow; 
my $label = $mw -> Label(-text=>"Hello World") -> pack();
my $button = $mw -> Button(-text => "Quit");
$button->bind('<ButtonPress-1>' => \&myexit);
$button->pack;

$button->eventGenerate('<ButtonPress-1>');

$mw->repeat(1000 => \&doit);

sub doit {
     $button->focus;
     $button->eventGenerate('<ButtonPress-1>');
}

MainLoop;

sub myexit
{
  print time."\n";
  #exit;
}

    [download]
    I'm not really a human, but I play one on earth. ..... an animated JAPH
[reply]
[d/l]

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