in reply to Tk: Binding Keys to events

Hi tamaguchi,

Note that you don't have to pass the subroutine as an anonymous subroutine within a list reference.

That is to say, although it will work to do: 

$mw->bind( '<Control-KeyPress-a>',   [sub {print "Button a has been pr
+essed\n"}] );
$mw->bind( '<Control-KeyRelease-a>', [sub {print "Button a has been re
+leased\n"}] );

[download]

One often specifies either a simple anonymous subroutine: 

$mw->bind( '<Control-KeyPress-a>',   sub {print "Button a has been pre
+ssed\n"} );
$mw->bind( '<Control-KeyRelease-a>', sub {print "Button a has been rel
+eased\n"} );

[download]

or a simple anonymous list: 

$mw->bind( '<Control-KeyPress-a>',   [ \&say_button_pressed,  "a" ]);
$mw->bind( '<Control-KeyRelease-a>', [ \&say_button_released, "a" ]);

# Unlikely to do it this way unless the following subroutines are
# longer, or likely to be called from multiple places...
#
sub say_button_pressed {
    printf "Button %s has been pressed\n", $_[0];
}
sub say_button_released {
    printf "Button %s has been released\n", $_[0];
}

[download]

I tend to use the former, an anonymous subroutine, when the code is brief and simple, whereas the latter is better when the subroutine is long and complex.

s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/

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Re^2: Tk: Binding Keys to events
by tamaguchi (Pilgrim) on Oct 03, 2006 at 10:43 UTC
    Thank you all. What is the rationale for having the syntax '<Control-KeyPress-a>' wouldn´t be more clear to write <KeyPress-Control-a>'?
[reply]
      It might well be more clear, but it doesn't work: 
      #!/usr/bin/perl -w
                                                                      
+          
use Tk;
                                                                      
+          
use strict;
use warnings;
                                                                      
+          
my $mw = new MainWindow();

$mw->bind( '<KeyPress-Control-a>', sub {print "Button a has been press
+ed\n"} );
$mw->bind( '<KeyPress-Control-a>', sub {print "Button a has been relea
+sed\n"} );

MainLoop;

# Produces ...
bad event type or keysym "Control" at
/usr/lib/perl5/site_perl/5.8.0/i386-linux-thread-multi/Tk/Derived.pm l
+ine 469.

# My version of Perl
This is perl, v5.8.0 built for i386-linux-thread-multi

      [download]
      s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/
[reply]
[d/l]
        This program creates a yellow rectangle on a canvas. The rectangle is possible to move up, down, left, and right by the respective arrow keys. 
          
#!/usr/bin/perl -w            
use Tk;
use strict;  
      
my $mw = MainWindow->new;
my $c = $mw->Scrolled('Canvas',
-width => 200,
-height => 200,
-background =>'blue',
-scrollregion => [ 0, 0, 500, 500 ]
);

$c->pack(-expand => 1, -fill => 'both');
my $rect=$c->createRectangle(100, 100, 150, 150, -fill => 'yellow');  
+    
    
    $mw->bind('<KeyPress-Left>', sub{$c->move($rect, -5, 0);});
    $mw->bind('<KeyPress-Right>', sub{$c->move($rect, 5, 0);});
    $mw->bind('<KeyPress-Up>', sub{$c->move($rect, 0, -5);});
    $mw->bind('<KeyPress-Down>', sub{$c->move($rect, 0, 5);});
    
    my @coords_list = $c->coords($rect);

MainLoop;

        [download]
        Now I would like to be able to move the rectangle on the diagonal by pressing for example both up and right. To write: 
        $mw->bind('<Right-KeyPress-Up>', sub{$c->move($rect, 5, -5);});

        [download]
        ..is however not possible do you have any other suggestions how to bind two arrowkeys to an event?
[reply]
[d/l]
[select]
        Hi tamaguchi,

        No, there's no way to do it using multiple keypresses (that I'm aware of).  And even if you could, there would be a problem when you held the 2 keys down, and relied on key repeats; whichever key you pressed "last" will dictate the direction that the object moves in.

        You can try it yourself by holding down the left and up arrow, for example; the initial movement might appear to be a "wobbly" northwest movement, but after the repeat kicks in, the square will only move left or up.

        My recommendation would be to assign a completely different set of keys.  For example, you could use the 8 keys centered around the "k": 

            my $pbindings = {
        'Key-j'  => sub { $c->move($rect, -5,  0) },
        'Key-l'  => sub { $c->move($rect,  5,  0) },
        'Key-i'  => sub { $c->move($rect,  0, -5) },
        'comma'  => sub { $c->move($rect,  0,  5) },
        'Key-u'  => sub { $c->move($rect, -5, -5) },
        'Key-o'  => sub { $c->move($rect,  5, -5) },
        'Key-m'  => sub { $c->move($rect, -5,  5) },
        'period' => sub { $c->move($rect,  5,  5) },
    };
                                                                      
+          
    map { $mw->bind("<$_>" => $pbindings->{$_}) } (keys %$pbindings);

        [download]
        s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/
[reply]
[d/l]

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