Cannot get canvas widget to bind keyboard event

[mbitzko]

I can get a canvas widget to honor a mouse event, but cannot get it to invoke a keyboard event. What I want to do is tie a function key <F4> to a zoom function in the canvas. But I cannot key a simple keypress or <F3> to work.

canvas $frame.worksp -width $cwidth -height $cheight \
-borderwidth 2 -relief sunken -background black
pack $frame.worksp -side bottom -expand yes -fill both
set worksp $frame.worksp
bind $worksp <ButtonPress-3> { puts "This works" }
bind $worksp <KeyPress> { puts "This fails" }

 

[Bong]

I think keypress events can only be bound in widgets where keyboard entries make sense; that is, in entry and text widgets. As an experiment, I can pack a frame: say .a, a label: .a.b, and an entry: .a.c.

If I bind: bind .a <Control-b> {.a.b configure -text done}, it won't matter whether my cursor is in the entry, and therefore in the frame, the binding does nothing.

If, on the other hand, I bind: bind .a.c <Control-b> {.a.b configure -text done}, then if I hit control&"b" when my cursor is in the entry, the label gets configured.

All of which is to say, I don't think it makes sense to bind a keypress event to a canvas.

_________________
Bob Rashkin

 

[ulis]

You need to give focus to the canvas before sending it key events:

  package require Tk
  grid [canvas .c]
  bind .c <F4> { tk_messageBox -message F4 }
  focus -force .c

Happy tecling

ulis

 

[ulis]

Have a look at the canvas man page :

http://www.tcl.tk/man/tcl8.4/TkCmd/canvas.htm

and the bind section:

"The only events for which bindings may be specified are those related to the mouse and keyboard"

"Keyboard-related events are directed to the focus item, if any (see the focus widget command below for more on this)."

For bind and focus, see:

http://www.tcl.tk/man/tcl8.4/TkCmd/bind.htm

http://www.tcl.tk/man/tcl8.4/TkCmd/focus.htm

For more on each command:

http://wiki.tcl.tk/canvas

http://wiki.tcl.tk/bind

http://wiki.tcl.tk/focus

ulis