Skip to Main Content
Learning Perl/Tk
book

Learning Perl/Tk

by Nancy Walsh
January 1999
Beginner content levelBeginner
373 pages
9h 43m
English
O'Reilly Media, Inc.
Content preview from Learning Perl/Tk

16.19. Waiting for Events to Happen

At certain points in your application, it makes sense to wait until something happens. For instance, if you create a ColorEditor window and want it to assign the color the user selects to a variable, you can use waitVariable to wait until the variable is set.

To have a program wait until a variable's value is changed, call waitVariable:

$widget->waitVariable(\$var);

Processing will continue as soon as the value contained within $var is changed to something different. To wait until a $widget is visible, use waitVisibility:

$widget->waitVisibility();

To wait until a widget is destroyed, call waitWindow:

$widget->waitWindow();

When you call these methods, nothing will happen in your program until the requested for event has taken place.

An alternative to waitWindow is OnDestroy, where you specify a callback. The widget methods are still available when you use OnDestory:

$widget->OnDestroy(sub { ... });

16.19.1. File Events

There is a special method in Perl/Tk called fileevent. You can use it to watch and be notified when a file is readable or writable. Here is an example snippet of code that shows how it can be used (this code is meant to be executed on a Unix system because we use the Unix tail command):[1]

[1] Thanks to my friend Phivu Nguyen for sharing his code with me.

use Tk; open (FH, "tail -f -n 25 text_file|") || die "Could not open file!\n"; my $mw = MainWindow->new(); my $text = $mw->Scrolled("Text", -width => 80, -height => 25)->pack(-expand ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Mastering Perl/Tk

Mastering Perl/Tk

Stephen Lidie, Nancy Walsh

Publisher Resources

ISBN: 1565923146Supplemental ContentCatalog PageErrata