Perl Cookbook

Responding to Tk Resize Events

Problem

You’ve written a Tk program, but your widget layout goes awry when the user resizes their window.

Solution

You can prevent the user from resizing the window by intercepting the Configure event:

use Tk;

$main = MainWindow->new();

$main->bind('<Configure>' => sub {
    $xe = $main->XEvent;
    $main->maxsize($xe->w, $xe->h);
    $main->minsize($xe->w, $xe->h);
});

Or you can use pack to control how each widget resizes and expands when the user resizes its container:

$widget->pack( -fill => "both", -expand => 1 );
$widget->pack( -fill => "x",    -expand => 1 );

Discussion

By default, packed widgets resize if their container changes size —they don’t scale themselves or their contents to the new size. This can lead to empty space between widgets, or cropped or cramped widgets if the user resizes the window.

One solution is to prevent resizing. We bind to the <Configure> event, which is sent when a widget’s size or position changes, registering a callback to reset the window’s size. This is how you’d ensure a popup error-message box couldn’t be resized.

You often want to let the user resize the application’s windows. You must then define how each widget will react. Do this through the arguments to the pack method: -fill controls the dimensions the widget will resize in, and -expand controls whether the widget’s size will change to match available space. The -expand option takes a Boolean value, true or false. The -fill option takes a string indicating the dimensions ...