re-binding Tab in a TK Text field

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

This is driving me crazy. I have a text field that I have absolutely no interest in ever entering an actual tab character into. I want Tab to shift the focus to the next widget, but I cannot get this to work. I have the following code:

my $t1 = $mw->Text(
       -background=>"navy",
       -foreground=>"white",
       -height=>35,
       -width=>80,
       -wrap=>"word",
       -selectbackground=>"blueviolet"
       );
my $e2 = $mw->Entry(
       -background=>"navy",
       -foreground=>"white",
       -width=>80,
       -textvariable=>\$description,
       -selectbackground=>"blueviolet"
       );
$t1->bind("<Tab>", sub { $e2->focus });
[download]

Now I have replaced Tab with Ctrl-q, and then when I Ctrl-q I get a control character printed, and the desired focus shift. But when I go back to Tab, I get a tab, and no focus shift. What do I have to do to rebind Tab to my wishes? If it's not possible to rebind Tab, how do I bind a character without the character printing in my Text field?

Believe nothing, no matter where you read it, or who said it - even if I have said it - unless it agrees with your own reason and your own common sense.
(Buddha)

Comment on re-binding Tab in a TK Text field Download Code

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Re: re-binding Tab in a TK Text field by kvale (Monsignor) on Oct 29, 2004 at 17:16 UTC
As you have found, Tab is special inside Tk::Text and your binding is not being trapped in time. I don't know why the explicit bind is not working. Mastering Perl/Tk mentions that the usual Tab focus method has been remapped to Shift-Tab for Tk::Text, so you might just use that. A more involved possibility is to derive a new subclass from Tk::Text that doesn't remap Tab. Look at Tk::ROText for an example of subclassing. It is probably just a matter of overriding a single method. -Mark	[reply]
Re^2: re-binding Tab in a TK Text field by pg (Canon) on Oct 29, 2004 at 18:02 UTC
I tested, and it was actually remapped to both CTRL-TAB and SHIFT-TAB. But I really hate the fact that it was remapped to SHIFT-TAB, as everybody knows that, TAB goes to the next field, and SHIFT-TAB goes back to previous field. Tk has no reason to break that convention.	[reply]
Re^3: re-binding Tab in a TK Text field by aquarium (Curate) on Oct 29, 2004 at 22:09 UTC
As a workaround, chop the last character off the text field variable in the exit field binding method. the hardest line to type correctly is: stty erase ^H	[reply]
Re^2: re-binding Tab in a TK Text field by wolfger (Deacon) on Oct 29, 2004 at 17:44 UTC
Actually, the normal Tab funciton is mapped to Ctrl-Tab, not Shift-Tab. At least, for Win32. I haven't tried it at home on Linux yet. Shift-Tab is normal Shift-Tab behaviour (backwards tabbing). Thanks for the pointer on subclassing. I'll check it out. -- Believe nothing, no matter where you read it, or who said it - even if I have said it - unless it agrees with your own reason and your own common sense. (Buddha)	[reply]
Re: re-binding Tab in a TK Text field by kelan (Deacon) on Oct 30, 2004 at 06:02 UTC
Ok, this is kind of tricky, but possible. In Tcl, you could do it like this: `bind .t1 <Tab> { focus [tk_focusNext .t1]; break }` [download] So you might think that a straight translation of that would work for Perl/Tk, but it doesn't. (I tried it.) The reason that a straight translation doesn't work is because Perl/Tk changed the default order that `bindtags` uses. To change the binding, either subclass and change it, as suggested above, or simply reorder the bindtags for the widget and then you can do the rebind: `# fix the bindtags order so that widget events are # processed before class events $t1->bindtags( [ ($t1->bindtags)[1,0,2,3] ] ); # now give the text widget a new Tab binding $t1->bind( '<Tab>', sub { $t1->focusNext; Tk->break; } );` [download] If you're observant, you'll also notice one other place where it wasn't a straight translation. In Tcl, `tk_focusNext` just returns the name of the next widget in focus order, then you have to actually call `focus` on it. In Perl/Tk, it just sets the focus directly.	[reply] [d/l] [select]
Re^2: re-binding Tab in a TK Text field by wolfger (Deacon) on Nov 03, 2004 at 15:00 UTC
Thanks! That does the trick, and is a lot easier than subclassing. -- Believe nothing, no matter where you read it, or who said it - even if I have said it - unless it agrees with your own reason and your own common sense. (Buddha)	[reply]


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